Kinesiology and Health Sciences

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This is the collection for the University of Waterloo's Department of Kinesiology and Health Sciences. It was known as the Department of Kinesiology until January 2021.

Research outputs are organized by type (eg. Master Thesis, Article, Conference Paper).

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Now showing 1 - 13 of 13

The aging spine: The effect of cyclic loading, simulated degeneration and prolonged sitting on joint stiffness across age
(University of Waterloo, 2018-08-22) Gruevski, Kristina May; Callaghan, Jack
Background: Low back pain is estimated to have a lifetime prevalence as high as 84%, and both the severity and frequency of low back pain reporting have a dependency on age. The nucleus pulposus and annulus fibrosis of the intervertebral disc undergo significant structural and compositional changes with increases in age. As the Canadian working population ages, an understanding of mechanical properties of spine tissue across age is needed to understand pain generating pathways and functional changes. The aim of this thesis was to determine if spine stiffness changes with age and to determine how the mechanical properties of the osteo-ligamentous spine and the annulus contribute to these changes in different loading scenarios. The thesis implemented both in-vitro (Studies I and II) and in-vivo (Studies III and IV) approaches to meet the objectives of the global thesis question. Study I: The effect of age and a cyclic loading protocol on the stiffness in porcine functional spine units (FSUs) was explored in study I. A total of 40 FSU specimens, with 21 young (aged 6-8 months) and 19 mature (aged 1.5-8 years) were cyclically loaded at 1 Hz to a range of motion of 8.5 degrees in flexion and extension around the midpoint of each specimen’s neutral zone for 3000 cycles with 1400 N of compression. Neutral zone stiffness was reduced in all specimens following the cyclic loading protocol, indicating no significant differences in temporal responses to repetitive loading across age. However, mature specimens were found to have greater neutral zone stiffness at both the C34 and C56 levels compared to younger specimens. This baseline differences between older and younger spines may alter load distributions in the disc and predispose mature discs to different types of injuries compared to younger specimens. Study II: The aim of study II was to isolate stiffness changes in isolated samples of the annulus in response to simulated aging. Low pH in the disc caused by lactic acid has been linked with cell death in the nucleus, discogenic pain and is a hypothesized initiator of disc degeneration. A total of 79 multilayer samples of porcine annulus fibrosis tissue obtained from young (aged 6-8months) spines were immersed in one of four pH and concentration controlled solutions of lactic acid in phosphate buffered saline (PBS) for a duration of 6 hours. The solutions included; (i) pH 7.2 PBS, (ii) pH 3.5 Lactic acid in PBS (15 mmol/L), (iii) pH 6 Lactic acid in PBS (15 mmol/L) or (iv) pH 7 Lactic acid in PBS (15 mmol/L). Following immersion, Specimens were biaxially loaded in tension in both the circumferential and axial directions to 20% strain at a rate of 2%/cycle for 100 cycles. The results of the study showed that circumferential peak stress was significantly higher in C56 specimens immersed in pH 3.5 solution compared to other solution groups. Circumferential stiffness was higher in the C56 specimens in a low pH 3.5 environment compared to the other solution groups. Exposure to a low pH environment altered the mechanical properties of the annulus fibrosis, including higher peak stress and increased stiffness. These changes demonstrate that the annulus is a contributor to increased spine stiffness changes with age. Furthermore, discs with accumulated lactic acid also have an altered mechanical environment that could put older discs at greater risk of annulus damage, such as delamination or fissures in the tissue. Study III: The purpose of study III was to determine the effect of age on lumped passive trunk stiffness, postures and discomfort responses during prolonged seated exposures. Participants in Studies III and IV were collected in the same session and shared a common cohort of 34 participants across younger and older age groups, with average (standard deviation) ages of 23.8 (5.0) years and 63.7 (3.9) years, respectively. Passive torso stiffness was measured in flexion before and after sitting continuously (90 minutes) while completing a controlled task on a desktop computer. Discomfort was reported to be higher among older adults in the neck, right shoulder and middle back regions during the prolonged sitting protocol compared to younger adults. There were no significant differences in passive torso stiffness between older and younger adults in flexion postures representing 10%, 20% and 30% of maximum. However, during the sitting protocol, younger adults adopted 19 degrees more flexion compared to older adults. Differences in seated postures across age may be explained by changes to passive tissues in older adults that affect the end range of functional motion, which may have implications for acute pain development during sitting. Study IV: The aim of study IV was to determine the effect of participant age, prolonged sitting and lift type on peak thoracic, lumbar, hip and knee postures and ratings of perceived effort. A secondary purpose was to quantify the effect of age on baseline lumbar range of motion about the mediolateral axis. All lifting tasks were floor to knuckle lifts and included, (i) 7 kg symmetrical, (ii) 4.5 kg symmetrical and (iii) 4.5 kg asymmetrical (box located 45 degrees to participant right). Lifting tasks were completed before and after the prolonged sitting protocol. The results of the study demonstrated lower peak lumbar flexion angles following 90 minutes of continuous sitting compared to prior to sitting. While there was no age-related difference noted in response to the prolonged sitting protocol, reduced peak flexion during the lifting tasks following sitting could represent swelling of the intervertebral disc in response to static sitting. Older adults adopted 12 degrees less lumbar flexion during the performance of all lifting tasks compared to younger adults. Older adults had reduced maximum range of motion about the mediolateral axis in the flexion direction compared to younger adults. However, when peak lumbar angles during lifting were expressed as a percentage of maximum flexion, angles were similar between groups with an average 71% and 65% among young and mature participants respectively. This could indicate that functional range of motion in the spine is reduced in older adults, with high flexion tasks entering a zone of higher stiffness. General Conclusions: Together, the findings from this thesis indicate that osteo-ligamentous functional spine units and the annulus increase in stiffness with age providing a mechanistic understanding of age-related mechanical changes to disc tissue. These changes may partially contribute to the reduction in maximum range of low back motion observed in older adults. Lumped passive stiffness was not significantly different at low flexion postures, but, maximum range of spine motion and peak flexion angles during high flexion tasks were reduced with increasing age. Higher stress in the posterior annulus of aged specimens could predispose older adults to greater risk of annulus disruption and could be a potential source of discogenic low back pain.
Assessing pre-existing movement and muscular recruitment differences in prolonged standing, transient low back pain developers compared to non-pain developers
(University of Waterloo, 2018-09-26) Park, Jonathan; Callaghan, Jack
Epidemiological studies have reported occupational prolonged standing to be associated with low back pain (LBP). Studies that have conducted simulations of prolonged standing work in healthy individuals have demonstrated a proportion of them will develop transient LBP (termed pain developers or PDs), while others will not (termed non-pain developers or non-PDs). Investigations into differences between pain groups using low-demand tasks have predominantly reported neuromuscular differences involving the hip musculature and have shown capacity to distinguish pain groups. However, misclassification persists. There is little published data on pain groups in response to higher-demand challenges, which may elicit previously unseen or larger differences. Thus, the purpose of this study was to examine movement behavior and muscle recruitment patterns in healthy individuals that are non-PDs or PDs during a variety of tasks with increased functional demand and variety. It was hypothesized that the higher demand challenges will elicit previously unseen or enhanced differences in movement behavior and muscle recruitment in PDs relative to non-PDs. Healthy university students were recruited to participate in two sessions. The first session involved participants performing a prolonged standing work simulation to determine their pain status. The second session involved participants performing a movement screening protocol involving low and high demand variations of the following tasks: symmetric trunk flexion-extension, symmetric floor-to-knuckle lift, modified star excursion balance test, active hip abduction, and reverse side bridge. Participants were outfitted with 3D motion capture markers and surface electromyography prior to task performance. Depending on the task, the kinematic data of the trunk and lower limbs were characterized into the following dependent variables: thorax segment angular velocity, peak lumbar spine flexion angle, frontal plane knee excursion, limb length normalized reach distances, and movement arc length. Depending on the task, surface electromyography of the external obliques, lumbar erector spine, gluteus medius, and gluteus maximus muscles were processed into the following dependent variables: phase lags at maximum correlation between muscle pairs and regression slope of median power frequencies for assessment of muscle fatigue. A total of 39 participants were recruited and categorized, resulting in a subtotal of 22 non-PDs (12 females) and 17 PDs (8 females). Mixed-design analysis of variance analyses revealed no statistically significant main or interaction effects between pain status groups in most of the aforementioned kinematic and surface electromyography dependent variables. Interestingly, performance during the active hip abduction (AHA) revealed a pain status and task difficulty interaction effect (F(1,35) = 5.22, p < 0.05), with PDs exhibiting larger angular displacement arc length during AHA performance with an external weight relative to no external weight; not observed in non-PDs. The results of this investigation showed that although task demands demonstrated changes in various kinematic and muscle activation patterns across participants, it did not always coincide with an individual’s pain status. Nonetheless, a significant finding to emerge from this study is the potential interaction an external weight has on pain status with their performance during the AHA. Taken together, these results suggest that there is minimal evidence for tasks with increased functional demand and variety to elicit unseen or larger aberrant movement behavior and muscle activation patterns in PDs relative to non-PDs.
Axial twist of the lumbar spine: Mechanical responses to twisted postures and potential factors for workplace injury
(University of Waterloo, 2017-08-24) McKinnon, Colin; Callaghan, Jack
While a link between magnitudes of spinal axial twist motions and the various modes of associated injury, pain reporting, and lost time claims has been tentatively established, there is need for greater investigation and understanding of the mechanical impact of axial twist motions. Researchers have compiled data sets demonstrating the relationship between twisting motions and moments and low back injury outcomes, but do not create a link to gross occupational exposures. Further, few studies can create a direct relationship between workstation design, trunk postures, and spine joint specific pain and failure mechanisms. When this limited mechanistic understanding is paired with injury prevalence statistics, they highlight a clear need to investigate the role of tissue-level axial twist exposures on occupational injury risk and workstation design guidelines to mitigate that risk. The global objective of this research was focused on developing a relationship between working axial twist postures and intervertebral joint injury risk. The four specific questions asked were (1) What is the relationship between externally measured thoracopelvic axial twist and the actual segmental axial twist motion of the intervertebral joints? (2) Can we use ultrasound as a modality to consistently and accurately measure vertebral axial twist motion? (3) What amount of lumbar axial twist presents an elevated injury risk for working populations? (4) What movement strategies do people use to perform reaching tasks at different hand locations, and how do task parameters impact these strategies? Study 1: Ultrasound has the potential for use to evaluate boney movement during axial twist of the lumbar spine in both in vivo and in vitro evaluations. Such segmental rotations could then be measured under controlled external thoracic axial twist conditions and in response to mechanical loading. The purpose of this study was to measure vertebral segmental rotations in a porcine model of the human lumbar spine using an ultrasound imaging protocol, and to validate use of this imaging technique with an optical motion capture system. Twelve porcine functional spinal units were fixed to a mechanical testing system, and compression (15% of compressive tolerance), flexion-extension, and axial twist (0, 2, 4, or 6 degrees) were applied. Axial twist motion was tracked using an optical motion capture system and posterior surface ultrasound. Correlation between the two measurement systems was greater than 0.903 and absolute system error was 0.014 across all flexion-extension postures. These findings indicate that ultrasound can be used to track axial twist motion in an in vitro spine motion segment and has the potential for use in vivo to evaluate absolute intervertebral axial twist motion. Study 2: The relationship between externally measured and internal spine axial twist motion is not well understood. Ultrasound is a validated technique (Study 1) for measurement of vertebral axial twist motion and has the potential for measuring segmental vertebral axial twist in vivo. The purpose of this study was to evaluate lumbar segmental axial twist in relation to external thoracopelvic twist using an ultrasound imaging technique. Sixteen participants kneeled in a custom-built axial twist jig which isolated motion to the lumbar spine. Participants twisted from neutral to 75% of maximum twist range of motion in an upright flexion-extension posture. Thoracopelvic motion was recorded with a motion capture system and L1 to S1 vertebral axial twist was recorded using ultrasound. Maximum thoracopelvic axial twist motion was 41.1 degrees. The majority of axial twist motion occurred at the L2-L3 (46.8% of lumbar axial twist motion) and L5-S1 (33.5%) intervertebral joints. Linear regression fits linking axial twist at each vertebral level to thoracopelvic axial twist ranged from 0.43 to 0.79. These findings demonstrate a mathematical relationship between internal and external axial twist motion, and suggest that classic use of L4-L5 to represent lumbar spine motion may not be appropriate for axial twist modeling approaches. Study 3: Axial twisting exposures have been repeatedly identified as a risk factor for occupational low back pain and injury, but there is a need for an improved understanding of the role of axial twist magnitude and associated moment as modifiers of the cumulative load tolerance of intervertebral joints. The purpose of this study was to mathematically characterize the relationship between axial twist motion magnitudes and the cumulative load tolerance of porcine cervical functional spinal units. Twenty-four porcine functional spinal units were fixed in a mechanical testing system under compressive load (15% of compressive tolerance) and in a neutral flexion-extension posture. Specimens were axially twisted to 5, 7.5, 10, 12.5, 15 or 17.5 degrees at 1 Hz until failure or 21 600 total cycles. Cumulative applied axial twist was recorded, and exponential functions were fit to the twist magnitude-cumulative twist moment recordings. Weighting-factor functions for cumulative axial twist moment injury risk were developed based on absolute axial twist magnitude and twist normalized to maximum range of motion. The non-linear weighting-factors have potential use in assessment of cumulative axial twist injury risk in occupational tasks. Study 4: The magnitude of axial twist in the lumbar spine in relation to reaching tasks is currently unknown. Therefore, the purpose of this study was to investigate lumbar spine axial twist during simulated occupational tasks across a range of forward and lateral reach distances, task heights, and exertion directions. Twenty-four participants performed single-handed, right-handed exertions against a load cell in three directions (upward, downward, forward push), at two heights (shoulder, elbow), and at 11 different hand target locations corresponding to current ergonomic reach guidelines. Thoracopelvic and right upper limb postures were recorded using an optical motion capture system, and trunk muscle activation was recorded using surface electromyography. Participants performed a contralateral twist at both the thoracopelvic spine and pelvis about the feet for directly forward hand targets, and twisted up to 19.9 degrees and 12.1 degrees at the lumbar spine and pelvis, respectively, at the most lateral hand target locations. Lumbar flexion and shoulder elevation each increased with reach distance to a maximum of 5.6 degrees and 64.9 degrees, respectively, at the furthest, directly forward hand target location. Hip and abdominal muscle activation exceeded 10% MVC for the most lateral hand target locations, and exhibited the highest activation for upward and forward push exertions. These findings suggest that future ergonomics guidelines should assess reaching and exertion tasks to hand target locations beyond 60-degrees from the midline of the body and consider them as non-optimal zones. The collection of studies in this thesis was structured to improve current ergonomics reach guidelines and provide a physiological and biomechanical basis for reach distance recommendations incorporating the low back. The findings from these studies have important implications for researchers, ergonomists, and clinicians assessing injury risk related to twisted occupational postures.
A Biomechanical-Biochemical Hypothesis for the Role of Collagen in Injury
(University of Waterloo, 2022-07-25) Barrett, Jeffery; Callaghan, Jack
Low back pain affects 80% of the population at some point in their lives and is the most common musculoskeletal complaint for workplace injuries. Further, it presents as episodic, with sufferers typically experiencing recurrent flares of symptoms. However, the mechanisms that underpin chronic, recurrent low back pain are still disputed, and many cases are paradoxically related to sedentary occupations. Therefore, this thesis explores whether the pathomechanics of low back pain may be partially explained in terms of extracellular matrix homeostasis with a particular focus on collagen. The balance of collagen synthesis, degradation, and mechanical disruption, mediated through an inflammatory response, is foundational for chronic degenerative diseases like tendonitis, osteoarthritis, and degenerative disc disease. Still, it is unclear whether the same pathways may be involved in recurrent low back pain. For this reason, this thesis formulates a mathematical model of this response, supported by three experimental studies that aim to describe the degradation and mechanical disruption properties of collagenous tissues. Some experiments have suggested that the rate of collagen disruption in collagenous tissues may be related to the strain rates they experience. However, there has yet to be an experiment to quantify this effect. Thus, the first experimental study in this thesis aimed to quantify whether the rate of damage accumulation is directly proportional to the strain rate. Fifty rat-tail tendon specimens were strained to failure, on one axis of a biaxial biological tissue testing apparatus (Cellscale, Waterloo, Ontario), at one of five strain rates: 0.01, 0.05, 0.10, 0.15 or 0.20 s−1. Force and displacement, later normalized to nominal stress and strain, were least-squares fit to a computational model of collagen fibril recruitment employing a Tobolsky-Eyring rate law to describe the rate of bond-breaking among the fibrils. Overall, the direct proportion constant increased linearly with the magnitude of the applied strain rate, yet the exponential parameter did not. Ultimately, this result suggested that the rate of collagen disruption in collagenous tissues may indeed be linearly related to the magnitude of strain rate. In response to potential damage to the extracellular matrix, the resident fibroblasts of soft tissues secrete inflammatory cytokines and matrix-degrading enzymes. Previous studies have suggested that mechanical strain to collagen may inhibit these enzymes, suggesting a potential remodelling mechanism that spares frequently used fibrils. Further, the stress-strain curve of biological tissues exhibits a prominent toe-region as a higher proportion of collagen fibrils become engaged. However, this mechanism implies that the activity of collagenases would be proportionately inhibited throughout the toe region. Thus, this study explored whether this graded inhibition of collagenases would occur for tissues held at loads corresponding to specific proportions of collagen fibrils being uncrimped. Ninety-two rat tail tendon samples were mounted along one axis of a biaxial biological tissue testing apparatus (Cellscale, Waterloo, Ontario), immersed in a Ringer’s solution bath heated to 37◦C with or without the presence of collagenase from C. histolyticum. Their forceelongation curves were measured, and its derivative evaluated to determine instantaneous stiffness-elongation. Tendons were held at levels of force corresponding to 0, 25, 50, 75 and 100% of the linear region’s stiffness, corresponding to approximately that proportion of collagen being uncrimped, for two-hours. Following this exposure, tendons were strained to failure at 0.2 s−1, and the change in linear region modulus was evaluated. Linear regressions between applied strain and the change in tissue stiffness suggested that mechanical strain proportionately inhibited the activity of collagenases inside the toe region. These results supported the proposed fibril selection hypothesis and were consistent with the fibril recruitment model. Several experimental studies have documented inflammatory responses downstream of repetitive lifting and cyclic loading in rat-tail intervertebral discs. These inflammatory responses precede the synthesis of matrix-degrading enzymes, which may contribute to a substantive feedforward inflammatory loop. However, none of these experiments have aimed to detect an inflammatory response downstream of a static flexion-induced creep on the intervertebral disc. Therefore, the purpose of this experiment was to document an inflammatory response in the rat-tail intervertebral disc downstream of a statically applied moment. Sixty rats were assigned to one of four time points (0, 8, 24, and 72 hours), two loading conditions (15 or 75 Nmm), or control for nine total groups. A robotic arm (Yaskawa Inc., Japan) applied a static moment to the caudal motion segment between vertebrae 8 and 9 of the experimental groups, at the specified loading magnitude, for one hour. Before and immediately after this creep protocol, the robotic arm determined the passive moment-angle curve of the motion segment. After waiting the prescribed time for each timepoint group, their passive moment-angle curves were measured again, the animals sacrificed, and the annulus fibrosis harvested between Ca8-9. Western Blot analyses were conducted to measure IL-1β, MMP-1, MMP-8, and TIMP-1. Overall, despite a substantial initial lengthening of the neutral zone (12.0 to 25.9◦), the creep exposure had no longterm mechanical consequences. This response was similarly reflected in the physiological outcome measures, where there was no sign of an inflammatory or remodelling response downstream of the applied mechanical creep. Ultimately, these results suggested that cyclic loading, compression, or a higher magnitude exposure may be required to induce an inflammatory response downstream of mechanical loading. The final contribution of this thesis was the development of a mathematical model of collagen engagement, damage, synthesis, and enzymatic degradation. This model was divided into a mechanical model, which dealt with the sequential fibril engagement in the toe region and failure according to the earlier Tobolsky-Eyring rate law. The physiological model focused on modelling the response of the fibroblast to damage-sensing. The mechanical model reproduced many salient features of viscoelastic materials, like creep, stress-relaxation, hysteresis and rate-dependence. Further, with the Tobolsky-Eyring rate law, the model could reproduce many features of fatigue, like the S-N curve or the results of creep-rupture experiments. The physiological model predicted a tri-phasic response, with an initial pro-inflammatory wave, followed by an anti-inflammatory wave and a remodelling phase, which was consistent with the description of the acute inflammatory response but could not be calibrated to experimental data. This combined model predicted an inflammatory response downstream of mechanical exposure in a threshold-constant relationship. This thesis explored collagen homeostasis as a potential contributor to chronic low back pain pathomechanics. It successfully measured the strain-rate proportionality of collagen rupture and the strain inhibition of collagenases, both of which are related to the rates of degradation and mechanical disruption of extant fibrils. It also showed that mechanical creep in isolation might not be a sufficient inflammatory stimulus in the annulus fibrosis of the intervertebral disc. A pain-generating pathway stemming from a one-time creep exposure may not elicit a painful inflammatory response. The mathematical model developed based on this work predicted a threshold-constant adaptive response to mechanical loading, and the exposure to living rats may have been below this threshold. However, more experimental work is required to establish this effect rigorously. Ultimately, this thesis further elucidated the potential interplay between mechanical exposures and physiological responses.
Development of a full flexion 3D musculoskeletal model of the knee considering intersegmental contact and deep muscle activity during high knee flexion
(University of Waterloo, 2019-01-24) Kingston, David C.; Acker, Stacey; Callaghan, Jack
Habitual kneeling in high knee flexion postures is a risk factor for knee joint dysfunction yet critical parameters for modeling this range of motion remain unknown or untested in three dimensions. High flexion is defined as postures exceeding 120° at the knee joint to a maximum of approximately 165°. Specific occupational and ethnic populations that regularly use high knee flexion postures have increased prevalence of degenerative knee diseases. This could suggest a causal relationship between habitual kneeling and disease prevalence resulting from repeated exposures. Therefore, this thesis was designed to explore two critical components for high knee flexion biomechanical modeling: intersegmental (thigh-calf and heel-gluteal) contact forces and lower limb muscular activation patterns across the full range of knee flexion. The global objective of this work was to develop a 3D musculoskeletal (MSK) model of the knee to estimate tibial contact forces in high knee flexion postures for determining the effect of intersegmental contact on these calculations. Two experimental studies, verification against a ‘gold-standard’ dataset, and an application study supported this global objective. Study 1: The purposes of this study were: 1) to measure total intersegmental contact force magnitude and centre of force (CoF) location during six high knee flexion movements and 2) to define regression models, based on anthropometrics, for the estimation of intersegmental contact parameters. Fifty eight participants completed six high knee flexion movements while motion capture and pressure data from the right lower limb were recorded. High knee flexion movements had average peak total intersegmental contact force magnitudes ranging from ~50-200N or ~8-30 %BW. Intersegmental CoF locations were segregated between thigh-calf and heel-gluteal regions with CoF, at peak total force, being ~6.2 cm and ~32.7 cm distal from the functional knee joint center about the long axis of the femur respectively. Five parameters of intersegmental contact (onset, maximum knee flexion angle, total contact force, thigh-calf CoF, and thigh-calf contact area) were then assessed for anthropometric based regression model fit. Strong correlations and linear regression models were found for maximum knee flexion angle and thigh-calf CoF, but only moderate to weak results were found for all other intersegmental contact parameters. The overall poor fit and variance explained by the linear regression models for onset, total force, and contact area suggest further work is needed to provide estimations of these parameters for use in future modeling efforts. Study 2: The purposes of this study were: 1) to measure surface and fine-wire EMG activation profiles in six high knee flexion movements and 2) to establish if surface EMG sites can be used as a proxy for fine-wire activation profiles. Sixteen participants completed the same high knee flexion movements, and level walking, as study 1 while activation waveforms from three deep muscles—vastus intermedius (VI), adductor magnus (AM), and semimembranosus (SM)—were recorded using fine-wire electrodes for comparison to easily accessible surface sites. Average peaks of VI, AM, and SM fine-wire activations during high knee flexion movements were approximately 30, 85, and 35 %MVC respectively. None of the surface sites recorded satisfied our criteria to successfully model fine-wire recordings. This was largely due to the considerable variability of surface-indwelling comparisons between participants. Our findings would suggest that the use of fine-wire EMG to obtain representative activation waveforms from VI, AM, or SM may be required if isolated muscle/motor unit activity is needed. MSK model: A full range of knee motion MSK model was developed for the estimation of tibial contact forces. Verification of the MSK model was completed by calculating the error between tibial compressive force estimates and measurements from an instrumented knee implant (gold standard). Vertex based object files of participant bones and CAD files of implant components were obtained from a public repository for gold standard data with muscle geometry scaled from our MSK model. Tibial compression estimates strongly fit implant data shape during walking (R2 0.83), squatting (R2 0.93), and ‘bouncy’ walking (R2 0.74) with an RMSD of 0.47, 0.16 and 0.58 BW respectively. Qualitative assessments of recorded EMG and muscle force estimations showed poor agreement between time-series data. Therefore, the strong fit of MSK tibial compression estimates to gold standard data would suggest this model is phenomenological in nature and does not accurately represent neuromuscular control. Application: The purpose of this study was to quantify the effect of including intersegmental contact on external knee joint moments and tibial contact force estimations. This study used participant data collected from study 2. There was an average RMSD of 3.56, 0.16, and 0.06 %BW*HT in flexion/extension, ab/adduction, and int/external external moments respectively when considering intersegmental contact parameters. Reductions in external moments caused changes to mean RMSD tibial contact force estimates: 0.14 BW lower compression, 0.2 BW lower posterior shear, and 0.03 BW higher lateral shear. Muscle force estimates generally followed EMG waveforms in shape for vastii, gluteus medius, and AM with SM having an improved agreement using its indwelling signal compared to surface measurements. General conclusions: Intersegmental contact forces must be considered when reporting tibial contact forces during high knee flexion movements as significant reductions to tibial posterior shear and increases in lateral shear were observed. Further work is required to refine MSK models in these ranges of knee motion as pressure sensor technology and soft tissue artifact are considerable limitations. Measurement of populations who habitually perform these activities needs to be completed to assess the translation of these findings to appropriate individuals.
Effects of posture and trunk muscle coordination on multi-joint isometric lifting strength: Implications for individualised movement assessment and intervention
(University of Waterloo, 2024-08-30) Pinto, Brendan Luke; Callaghan, Jack
The manner in which movement is executed can influence biomechanical demand and consequently the development of musculoskeletal disorders. Although modifying movement execution can help regulate biomechanical demand by influencing tissue loading and tolerance, it can also influence physical performance by influencing the ability to exert force. Movement-based interventions to regulate biomechanical demand that hinder physical performance can limit acceptability, sustainability, and effectiveness of the intervention. Conversely, interventions to enhance physical performance that modify movement execution in a way that imposes higher than necessary biomechanical demand, can hinder physical development and long-term performance. However, the development of comprehensive movement assessments and interventions that consider both the impact on biomechanical demand as well as physical performance is challenged by a scarcity of knowledge of how movement execution can influence physical performance in multi-joint tasks. The global aim of this thesis was to investigate how modifying posture and trunk muscle coordination can influence the ability to exert force during isometric lifting. Four studies were conducted to address the global thesis aim. Study 1 investigated the effects of modifying trunk inclination and low back curvature on isometric lifting strength as previous research has yet to clearly dissociate how these distinct postural characteristics could influence the ability to exert force in multi-joint tasks such as lifting from the ground. Results showed that modifying trunk inclination and low back curvature can influence strength in multi-joint tasks substantially and to a similar extent. However, the effect of modifying these postural characteristics interact and vary greatly across individuals in magnitude (up to 620N of isometric lifting force) and direction (increase/decrease). Thus, a single postural profile cannot be generalized as the strongest for every individual and the ability to exert force in multi-joint tasks cannot be inferred solely from posture. Additionally, the individually varying effects of posture on strength suggests that individuals can adapt through movement training to be stronger in postures that are favourable for tissue loading and tolerance. Assessing the L4/L5 joint contact forces of the observed postures suggested that the effect of posture on biomechanical loading is more consistent, and the biomechanical demand imposed by flexing the low back outweighs any potential acute gain in isometric lifting strength. Together this supports the recommendation to avoid highly flexed low back postures during demanding physical activities. Study 2 compared the immediate effects of a simple verbal directive and detailed trunk muscle bracing coaching on isometric lifting strength, low back postural displacement and trunk muscle co-contraction. Prior research has suggested that cueing co-contraction of all the trunk muscles can enhance the ability to exert force in multi-joint tasks but has not yet isolated the effect of modifying trunk muscle coordination on the ability to exert force which may potentially depend on the approach used to cue trunk muscle coordination. Detailed coaching which included a combination of verbal and physical cues was more effective than the simple verbal directive at increasing trunk muscle co-contraction (group mean co-contraction for the baseline, directive and coached condition was 10.1%, 11.0% and 13.5% respectively) and decreasing low back postural displacement (group mean change in low back flexion angle normalized to each individual’s maximum flexion range-of-motion for the baseline, directive and coached condition was 21.4%, 19.5% and 17.2% respectively). However, both cueing approaches immediately reduced isometric lifting strength to a similar extent (group mean peak isometric lifting force for the baseline, directive and coached condition was 1194 N, 1109 N and 1096 N respectively). Results indicate that detailed coaching is more effective than simple verbal directives at modifying trunk muscle coordination to restrict low back postural displacement but cautions cueing trunk muscle coordination for the first time in situations where peak force production is desired. Results also suggest that future research should confirm acquisition and transfer of the targeted trunk muscle coordination patterns as the full potential impact of modifying trunk muscle coordination may not be completely apparent from observing the immediate responses to cues. Motivated by the individually varying effects of posture on the ability to exert force observed in Study 1, Study 3 evaluated the extent to which proxies for leverage derived from kinematic quantities can statistically explain the individual variation in the effects of posture on the ability to exert isometric lifting force. Prior research has used kinematic-based proxies to describe and make inferences about how posture can influence leverage in multi-joint tasks. However, these approaches do not capture all the mechanics involved in multi-joint kinetics and the extent to which they may explain the individually varying effects of posture on the ability to exert force in a multi-joint task has not yet been tested. As expected, based on fundamental biomechanical principles, the kinematic-based proxies for leverage that were investigated (joint-to-external force moment arms and predicted joint-angle-dependent torque-generating capacities) explained a very low proportion of variation (<17%) in the effects of posture on isometric lifting force. In contrast, variables derived from both kinematic and kinetic measurements such as the net joint reaction moments calculated using a rigid linked segment model and inverse dynamics explained a higher proportion of variation in the effects of posture on the ability to exert isometric lifting force (approximately 80%). These results indicate that simplified kinematic-based approaches cannot be used to assess the effects of posture on leverage in multi-joint tasks on an individual basis. Instead, variables derived from both kinematic and kinetic measurements such as the net joint reaction moments show promise for being used in development of quantitative assessments of multi-joint leverage. Study 4 investigated whether individuals maintain their potential for physical performance when given instruction to avoid rounding the low back during light mass lifting. Compared to prior movement-based interventions such as the squat lift technique that vaguely describes whole body posture, targeting a key postural feature such as low back flexion is theoretically expected to afford greater flexibility to self-organize the rest of the body linkage to regulate biomechanical demand, without hindering physical performance. However, using simple verbal directives to cue specific movement features during low demand tasks may not acutely prompt individuals to prioritize physical performance as they self-organize, rendering the intervention ineffective. Although aggregate group level results indicated that low back postural instruction targeting biomechanical demand decreased low back flexion during crate lifting and increased isometric lifting strength in postures replicating those exhibited during crate lifting, there was high heterogeneity in responses. Among the 37 of 40 participants classified as individuals who could potentially benefit from decreasing their low back flexion, 15 and 22 participants were respectively classified as successful and unsuccessful in decreasing low back flexion in response to the instruction, to be within a range that minimizes passive tissue strain. Though replicating the crate lifting posture to assess isometric strength emerged to be challenging, there were individuals who increased (n=8), decreased (n=9) and did not change (n=23) isometric strength, independent of their low back postural response. Hence, although most participants appeared to maintain physical performance potential when given simple verbal directives that target low back flexion to regulate biomechanical demand, some participants responded in a manner that decreased performance potential and many did not successfully decrease their low back flexion within a range that minimizes passive tissue strain. This suggests a need for more detailed movement coaching and training in research and practice to effectively modify movement behaviour without hindering physical performance potential. Overall, the results from this thesis indicate that the effects of modifying posture and trunk muscle coordination on the ability to exert force in multi-joint tasks is complex and can greatly vary across individuals. Additionally, modifying movement execution may need to go beyond simple verbal directives to provide detailed movement coaching. The findings support that considering the effects of movement execution on physical performance has the potential to advance movement assessment and intervention strategies. Yet, there is a need to develop approaches to capture the individually varying effects of movement features such as posture on the ability to exert force in multi-joint tasks to develop strategies that can effectively regulate biomechanical demand without hindering physical performance as well as enhance physical performance without imposing unnecessary biomechanical demands.
Effects of shoe midsole cushioning on low back impact shock attenuation in recreational runners
(University of Waterloo, 2023-09-22) Fok, Donna; Callaghan, Jack
Running is one of the most widely practiced and accessible forms of physical activity. When the foot contacts the ground during running, impacts on the order of two to three times body weight are generated. The impact force is attenuated by joints and propagated through each subsequent segment from the foot to the head over 600 times per kilometer and has been associated with the development of various pains and injuries across runners. Consequently, mechanisms of shock attenuation have been widely researched across the last few decades, where previous work has aimed to examine how joint positioning, eccentric muscle activation, passive soft tissue structures, and other strategies may help mitigate this impact on the musculoskeletal system. However, how these mechanisms are presented in the lumbar spine, which largely influence the delivery and experience of this impact shock in the upper body and head, is not well understood. Further complicating this area is the role of running shoe cushioning, or the midsole. Softer and thicker midsoles have been shown to interact with lower limb kinematics and muscle activation, contributing to differences in leg stiffness and shock attenuation. Therefore, it was hypothesized that more compliant midsoles would produce similar results in the lumbar spine. Specifically, the purpose of this study was to investigate if increased shock transmission and shock attenuation occurred in the lumbar spine in response to softer midsoles. It was further hypothesized that differences would exist in sagittal knee and lumbar flexion angles and trunk muscle activation across midsole cushioning stiffness as well as between sex. Twenty (10M, 10F) pain-free recreational runners who averaged a minimum weekly mileage of 16 km were recruited to participate in this study. Subjects were asked to run on a treadmill at 3.3 m/s for five minutes in each of three shoe conditions that ranged in their midsole cushioning stiffness, quantified prior to use in running via a mechanical testing system. Sagittal kinematics of the lumbar spine, pelvis, and right lower limb were collected using an active motion capture system, mean bilateral muscle activity, co-activation indices, and phase lags between co-activation of the lumbar erector spinae, rectus abdominus, and external obliques were measured via surface electromyography, and accelerometers were placed at the distal tibia, borders of the lumbar spine, and head to calculate peak resultant acceleration as well as shock attenuation in the frequency domain. All variables were calculated during stance phase and averaged across fifteen consecutive strides. Two-way mixed measures analyses of variances were used to assess differences across shoe conditions and between sexes. Softer and more compliant midsoles resulted in increased ankle plantarflexion and knee extension leading to differences in low frequency shock attenuation, but the low back was not particularly responsive to midsole stiffness. Similar tibial and lumbar spine acceleration magnitudes were observed across all midsole stiffness conditions, and neither lumbar posture nor trunk muscle activation and co-activation changed with footwear. Minor differences were observed between sex, suggesting that females may employ slightly different shock attenuation mechanisms particularly at the hips and lower limbs, but future investigations are necessary to better understand the specific shock attenuation mechanisms involved. Overall, these results add to the evidence that midsole cushioning stiffness may influence the lower limb but suggest that such changes are accommodated by the time the shock reaches the lumbar spine.
The Efficacy of an Ergonomics Education Program on Sit-Stand Workstation Usage Behaviours: A Field Intervention Study
(University of Waterloo, 2016-09-06) Riddell, Maureen; Callaghan, Jack
Abstract Background: Much is known about the negative aspects of sitting and standing for long periods of time. In recent years there has been a shift in office furniture from non-height adjustable workstations to those that fully accommodate sitting and standing whole body postures. In the past, the integration of sit-stand desks has shown positive but also negative consequences such as pain development or minimal use of the new workstation. Outcomes depend fundamentally on the training that new users of sit-stand workstations receive. Currently, there is no standardized training program provided to users on how they should integrate their new workstations into their day to ensure optimal use of the workstation. The objective of this research study was to determine if a training program that new users of sit-stand workstations received prior to their implementation could influence the long term usage of the workstations. It was hypothesized that the type of training program that individuals received would influence how much they would use the workstation over a period of two months, would influence reports of musculoskeletal discomfort, and influence mood states. Methods: Thirty-five adults between the ages of 23 and 64 were recruited from a University of Waterloo research centre to assess the influence of training program on the long term usage of sit-stand workstations. Participants were divided into 1 of 2 groups based on their job tasks, age and sex. A baseline period (Phase 1) was collected as participants worked at their original non height adjustable workstations. Both groups received an initial training program that was an example of what is currently taught in industry. The one group then received an additional session that focused on transitioning between sitting and standing and proper sitting and standing techniques. The first four weeks after the training sessions represented the intervention phase (Phase 2) of the study. During this time, those in the group who received the additional training program also received weekly meetings from the experimenter to answer any questions that the participants had regarding their workstation as well as daily reminders to rotate between sitting and standing in a 1:1 ratio. These meetings were stopped for the subsequent four weeks as this time period acted as the follow-up phase (Phase 3). Desk transitions from sitting to standing were tracked using tri-axial data logging accelerometers that were securely mounted to each participants’ desk (Gulf coast solutions, Waveland, Mississippi) and a measure of self-perceived sitting and standing throughout the day was taken using the Occupational Sitting and Physical Activity Questionnaire. Musculoskeletal pain score was collected on a nine point Likert scale. The Active Hip Abduction Test was collected at the beginning and end of the study to determine if any differences occurred between groups. Lastly, the Profile of Mood States questionnaire was collected to determine if any changes in mood states would occur throughout the study. Results: There was a main effect of group (p<0.0001) for the number of transitions completed each day. On average, those in the group that received the additional training session based on current best practice research transitioned 6.0 (±2.1) times a day whereas those who only received a training session that is currently delivered in industry transitioned 3.2 (±1.9) times each day. There was no main effect of phase (p=0.1161). There was a main effect of group p=0.0473 and phase p<0.0001 for self-reported time spent sitting each day as collected via the Occupational Sitting and Physical Activity Questionnaire. There was no effect of group or time on the musculoskeletal pain reported in the lower back, buttocks, and feet region. There was an influence of phase for neck pain and right and left shoulder pain. Group influence the percentage of days that pain was reported in the right and left shoulder regions. The percentage of days that pain was reported was higher for those who received the additional training session. Overall, those in the additional group reported sitting 6% less than those who received the industry example training. There was a main effect of group p=0.0401 and a main effect of period of p<0.0001 for self-reported time spent standing via the OSPAQ. Overall, those who received the additional training session reported standing 6% more than those who did not. Those who received the additional training session had fewer days where they did not use their workstation at all (p=0.0002). There was an influence of group on the mood state anger and depression. Those who received only the industry training session reported lower anger and depression scores by 1.3 and 1.2 respectively. Scores for confusion decreased in both groups as the study progressed (p<0.0001). There was no influence of group on the amount that participants walked each day as assessed by the Fitbit Zip (p=0.6934) and by the Occupational Sitting and Physical Activity Questionnaire (p=0.6174). There was an influence of outcome on the Active Hip Abduction Test (AHABD) on the number of days that pain occurred. Those who scored positive on the AHABD test reported more pain than those who scored negative. Discussion: Those who received the additional training session prior to using their sit-stand workstation transitioned more often than those who only received the training session that was an example of what is currently bring completed in the industry. They also reported less time spent sitting throughout the day and more time spent standing. One of the major problems with the implementation of sit-stand workstations, as reported by industry practitioners and researchers, is the discontinued use of sit-stand workstations as time progresses. The current study found that with the delivery of a training program that was based on current best research practice in the topic of sit-stand workstation usage, there were less days where the workstation was not used at all. Behaviour change techniques, motivational interviewing approaches and hands on practice with the workstation should be incorporated into future training programs to develop sustainable habits centered around whole body posture variation.
An EMG-Driven Cervical Spine Model for the Investigation of Joint Kinetics: With Application to a Helicopter Pilot Population
(University of Waterloo, 2016-09-16) Barrett, Jeffery; Callaghan, Jack
As the workforce has been shifting from manufacturing to office work, reports of neck pain have been on the rise. Unfortunately, the mechanism for the development of chronic neck pain still remains disputed. Most current cervical spine biomechanical models are aimed at the simulation of whiplash and are forward models employing the finite element method or multibody dynamics that are ill-equipped for incorporating motion capture data, with even fewer models capable of interfacing with electromyography (EMG) data. Therefore, there is a considerable opportunity to develop an inverse dynamic model that can drive muscle forces using EMG with the goal of determining the joint mechanics that could lend insight to the loading patterns and injury mechanics in the cervical spine. The current model is an inverse dynamic multi-body model of the whole cervical spine, head, and thorax. It was created entirely in Python, using anatomical data obtained from the Anatomography project, which were rescaled to match dimensions from a 50th percentile male. Constitutive expressions for ligaments are described by nonlinear springs, while the disc and facet joints are lumped into exponential rotational springs. Active muscle forces are estimated from EMG using a Hill-type muscle modeling framework. The model has endured a rigorous validation procedure comparing its predicted compression and shear values to a previously published model. The gains for each muscle were analyzed to evaluate how well muscle forces are being predicted from EMG. Finally, a sensitivity analysis was conducted to identify if the outputs of the model were overly dependent on the numeric value of a specific parameter. Overall, compression and mediolateral shear values were in good agreement with the previous model, while anteroposterior shear values were significantly smaller in magnitude. Despite this, muscle gains were, in some cases, alarmingly high. Finally, the sensitivity analysis revealed that the model is somewhat sensitive to ligament and muscle slack lengths, albeit to a much lesser extent than previously published models. The model was used to evaluate the change in joint kinetics with a flexed posture compared to a neutral one. With 45 degrees of flexion, compressive forces increased twofold throughout the cervical spine. In addition, anteroposterior shear tended to increase fourfold in the upper cervical spine, however, equalized with a neutral posture around the C4-C5 level. These findings may have implications for injury mechanisms, as a flexed posture under compression has been strongly associated with the development of posterior disc prolapse. In addition, the model was used to assess the joint kinetics from an existing data set on helicopter pilots who are required to wear night vision goggles during night flights. The classic solution to the anteriorly placed weight of the night vision goggles has been to counterbalance it with a posterior counterweight. While this works theoretically in a neutral posture, once a deviated posture is assumed, joint kinetics correspondingly increase. Adding a helmet increased the compression at C5-C6 from 204 N to 258 N, a 26% increase. Furthermore, adding night vision goggles and a counterweight increased it by 60%. Increasing the mass of the head-segment leads to an increase of compression.
Exploring Low to Moderate Velocity Motor Vehicle Rear Impacts as a Viable Injury Mechanism in the Lumbar Spine
(University of Waterloo, 2020-05-19) Fewster, Kayla; Callaghan, Jack
Epidemiological research suggests that up to 50% of individuals involved in low speed rear impact collisions develop acute onset low back pain. Given that little information is known about the low back injury mechanisms as a result of these collisions the overarching goal of this thesis was to explore low to moderate velocity rear-end collisions as a potential low back injury mechanism. Using a combination of data mining, in vivo and in vitro mechanical testing of porcine functional spinal units, the global purposes of this thesis were to (i) explore the types of low to moderate velocity collisions that frequently result in claims of low back pain and injury (ii) explore the influence of low velocity rear impact collisions on peak in vivo joint loading, occupant pain reporting and passive tissue response of the lumbar spine, and (iii) characterize the effects of these mechanical exposures and explore facet joint capsule injury as a potential source of injury and pain generating pathways following low to moderate severity impacts. In-line with these global purposes, four independent studies were conducted, each with their own focused objectives. Study I - Exploring Low Velocity Collision Characteristics Associated with Claimed Low Back Pain Background: Up to fifty percent of individuals involved in low to moderate velocity collisions report low back pain. However, our understanding of the specific collision or occupant characteristics that result in such claims of low back pain remains limited. Objectives: The primary objective of this study was to define the circumstances of low velocity motor vehicle collisions that result in litigation in Ontario with claims of low back injury. Methods: Data for this investigation were obtained from a forensic engineering firm based in Toronto, Ontario, Canada. The database was searched and only cases with an evaluation of the injuries sustained in passenger vehicle to vehicle collisions, with a collision severity of 24 km/hour or less were included in this analysis. Each identified case was reviewed for collision characteristics, pre-existing medical conditions and injuries claimed. Descriptive statistics (mean, SD and ranges) across low back injury claims were computed for documented variables. Results: Out the 83 cases reviewed, 77% involved a claim of low back injury. Specific to those who claimed low back injury, examination of the medical history revealed that pre-existing low back pain (LBP) or evidence of lumbar disc degeneration were particularly common with 63% of claimants either having had a history of LBP or evidence of lumbar disc degeneration, or both. Of all low back injury claims, 97% were accompanied by a whiplash and/or whiplash associated disorder claim. For low back injury claims, a rear-end impact was the most common configuration (70% of all low back injury claims involved a rear-end collision). The majority of all low back injury claimants experienced a change in velocity of 13 km/hour or less (69%), with 42% of all low back injury claims falling between collision severities of 10 – 12 km/hour. Conclusions: Results indicate that rear-end collision severities of 10 – 12 km/hour appear to be particularly common with respect to low back injury reporting; more severe collisions were not associated with greater low back injury reporting. This result contrasts with previously published neck injury risk data, which demonstrated the risk of neck injury symptom reporting increases with collision severity. Evidence of lumbar disc degeneration was particularly common across claimants with low back injury claims. Study II - Characterizing Trunk Muscle Activations During Simulated Low Speed Rear Impact Collisions Background: The internal forces generated by the musculature of the lumbar region create most of the mechanical load placed on the spine. Thus, despite the anticipated low external forces generated between the occupant and the automobile seatback during a low speed rear impact collision, increased muscle tension may influence the resultant peak joint loads experienced in the lumbar spine. Consequently, the risk of low back injury may be altered by muscle activation. Objective: The purpose of this study was to evaluate the activation profiles of muscles surrounding the lumbar spine during unanticipated and braced simulated rear-end collisions. Methods: Twenty-two low speed sled tests were performed on eleven human volunteers (△v = 4 km/h). Each volunteer was exposed to one unanticipated impact and one braced impact. Accelerometers were mounted on the test sled and participants’ low back. Six bilateral channels of surface electromyography (EMG) were collected from the trunk during impact trials. Peak lumbar accelerations, peak muscle activation delay, muscle onset time and peak EMG magnitudes, normalized to maximum voluntary contractions (MVC), were examined across test conditions. Results: While not statistically significant, bracing for impact tended to reduce peak lumbar acceleration in the initial rearward impact phase of the occupant’s motion by approximately 15%. The only trunk muscles with peak activations exceeding 10% MVC during the unanticipated impact were the thoracic erector spinae. Time of peak muscle activation was slightly longer for the unanticipated condition (unanticipated = 296 ms; braced = 241 ms). Conclusions: Results from this investigation demonstrate that during an unanticipated low speed rear-end collision, the peak activation of muscles in the lumbar spine are low in magnitude. As such, muscle activation likely has minimal contribution to the internal joint loads that are experienced in the lumbar intervertebral joints during low speed rear impact collisions. Study III - Characterizing In Vivo Mechanical Exposures of the Lumbar Spine During Simulated Low Velocity Rear Impact Collisions Background: Historically, there has been a lack of focus on the lumbar spine during rear impacts because of the perception that the automotive seat back should protect the lumbar spine from injury. As a result, there have been no studies involving human volunteers to address the risk of low back injury in low velocity rear impact collisions. Objectives: The primary objectives of this study were to explore lumbar kinematics and joint reaction forces in human volunteers during simulated rear impact collisions and to examine the influence of lumbar support on the peak motion and forces experienced in the lumbar spine. A secondary objective was to evaluate lumped passive stiffness changes and low back pain reporting after a simulated rear impact collision Methods: Twenty-four participants (12 male, 12 female) were recruited. A custom-built crash sled was used to simulate unanticipated rear impact collisions, with a change in velocity of approximately 8 km/h. Randomized collisions were completed with and without lumbar support. Measures of passive stiffness and flexion-relaxation-ratio (FRR) were obtained prior to impact (Pre), immediately post impact (Post) and 24 hours post impact (Post-24). LBP reporting was monitored over the next 24 hours leading up to the final Post-24 measures. For collision simulations inverse dynamics analyses were conducted, and outputs were used to generate estimates of peak L4/L5 joint compression and shear. From the passive trials, lumbar flexion/extension moment-angle curves were generated to quantify time-varying changes in the passive stiffness of the lumbar spine, Post and Post-24 relative to Pre. FRRs were computed as the ratio of thoracic erector spinae and lumbar erector spinae muscle activation in an upright posture to muscle activation in a flexed position Results: Average [± standard deviation] peak L4/L5 compression and shear reaction forces were not significantly different without lumbar support (Compression = 498.22 N [±178.0]; Shear = 302.2 N [± 98.5]) compared to with lumbar support (Compression = 484.5 N [±151.1]; Shear = 291.3 N [±176.8]). Lumbar flexion angle at the point of peak shear was 36 degrees [±12] without and 33 degrees [±11] with lumbar support, respectively, with 0 degrees being the lumbar posture in upright standing. No participants developed clinically significant levels of LBP after impact. Time was a significant factor for the length of the low stiffness flexion and extension zone (p = 0.049; p = 0.035), the length of the low stiffness zone was longer in the Post and Post-24 trial for low stiffness flexion and longer in the Post-24 for low stiffness extension. Conclusions: Findings demonstrate that during a laboratory-simulation of an unanticipated 8 km/hour rear-impact collision, young healthy adults do not develop LBP. Lumbar support did not significantly influence the estimated L4/L5 joint reaction forces. Changes in the low stiffness portion of the passive flexion/extension curves were observed following impact and persisted for 24 hours. Changes in passive stiffness may lead to changes in the loads and load distributions within the passive structures such as the ligaments and intervertebral discs following impacts. Study IV - Exploring the Interaction Effects of Impact Severity and Posture on Vertebral Joint Mechanics Background: To date, no in vitro studies have been conducted to explore lumbar soft tissue injury potential and altered mechanical properties from exposure to impact forces. Typically, after a motor vehicle collision, the cause of a reported acute onset of low back pain is difficult to identify with potential soft tissue strain injury sites including the facet joint and highly innervated facet joint capsule ligament (FCL). Objectives: The purpose of this investigation was to quantify intervertebral translation and facet joint capsule strain under varying postures and impact severities. A secondary objective was to evaluate flexion-extension and shear neutral zone changes pre and post impact. Methods: A total of 72 porcine cervical FSUs were included in the study. Three levels of impact severity (4g, 8g, 11g), and three postures (Neutral Flexion and Extension) were examined using a full-factorial design. Impacts were applied using a custom-built impact track which simulated impact parameters similar to those experienced in low to moderate speed motor vehicle collisions. Passive flexion-extension and shear neutral zone testing were completed immediately prior to and immediately post impact. Intervertebral translation and the strain tensor of the facet capsule ligament were measured during impacts. Results: A significant main effect (p > 0.001) of collision severity was observed for peak intervertebral translation and peak FCL shear strain (p = 0.003). A significant two-way interaction was observed between pre-post and impact severity for flexion-extension neutral zone length (p = 0.031) and stiffness (p>0.001) and anterior-posterior shear neutral zone length (p = 0.047) and stiffness (p>0.001). This was a result of increased neutral zone range and decreased neutral zone stiffness pre-post for the 11g severity impact (regardless of posture). Conclusions: This investigation provides evidence that overall the peak vertebral translations observed across 4g to 11g impacts are below previously published ultimate shear failure displacements. FSU’s exposed to the highest severity impact (11g) had significant NZ changes, with increases in joint laxity in flexion-extension and shear testing and decreased stiffness, suggesting that soft tissue injury may have occurred. Despite observed main effects of impact severity, no influence of posture was observed. This lack of influence of posture and small FCL strain magnitudes suggest that the FCL does not appear to undergo injurious or permanent mechanical changes in response to low to moderate MVC impact scenarios. Study V - Characterizing the Mechanical Properties of the Facet Joint Capsule Ligament Background: The facet joint capsule ligament (FCL) is a structure in the lumbar spine that constrains motions of the vertebrae. Previous work has demonstrated that under physiological motion the FCL is subjected to significant deformation with FCL strains increasing in magnitude with increasing flexion and extension moments. Thus, it is important to characterize the mechanical response of the FCL for investigations into injury mechanisms. Sub failure loads can produce micro-damage resulting in increased laxity, decreased stiffness and altered viscoelastic responses. Thus, the objective of this investigation was to determine the mechanical and viscoelastic properties of the FCL under various magnitudes of strain from control samples and samples that had been exposed to an impact. Objectives: The purpose of this investigation was to quantify the mechanical properties and viscoelastic response of control and impacted FCL. Methods: 200 tissue samples were excised from the right and left FCL of 80 porcine cervical functional spinal units (FSU’s). Tissue samples were excised from FSU’s obtained from Study 4. Twenty FCL tissue samples served as the control group. The remaining 180 FCL tissue samples were randomly obtained from FSU’s that had been exposed to one of nine impact conditions (impacted tissue). Each specimen was loaded uniaxially, collinear with the primary fiber orientation. The loading protocol was identical for all specimens: preconditioning with 5 cycles of loading/unloading to 5% strain, followed by a 30 second rest period, 5 cycles of 10% strain and 1 cycle of 10% strain with a hold duration at 10% strain for 240 seconds. The same protocol followed for 30% (cyclic-30% & 30%-hold) and 50% strain (cyclic-50% & 50%-hold). All loading and unloading were performed at a rate of 2%/sec. All impacted FCL properties were compared back to controls. Measures of stiffness, hysteresis and force-relaxation were computed for the 30% and 50% strain conditions. Results: No significant differences in stiffness were observed for impacted specimens in comparison to control (30% Control = 2.64 N/mm; 4 g = 2.20 N/mm, 8 g = 2.07 N/mm, 16 g = 2.16 N/mm)(50% Control = 5.06 N/mm; 4g = 4.60 N/mm, 8 g = 4.07 N/mm, 16 g =4.64 N/mm). Impacted specimens from the 8g Flexed and 11 g Flexed and Neutral conditions exhibited greater hysteresis during the cyclic-30% and cyclic-50%, in comparison to controls. In addition, specimens from the 8g and 11g Flexed conditions resulted in greater force relaxation for the 50%-hold conditions. Conclusions: Results from this study demonstrate viscoelastic changes in FCL samples exposed to moderate and highspeed impacts in the flexed posture. However, it is interesting that these viscoelastic changes were not accompanied by changes in stiffness. Findings from this investigation provide novel insight and provide mechanical and viscoelastic properties of the FCL both in control and impacted scenarios. Global Summary: Findings from this thesis demonstrate that (i) rear-end collision severities of 10 – 12 km/hour appear to be particularly common with respect to low back injury reporting (ii) during a laboratory-simulation of an unanticipated 8 km/hour rear-impact collision, young healthy adults do not develop LBP, however, changes in the low stiffness portion of the passive flexion/extension curves were observed following impact and persisted for 24 hours and (iii) the observed peak displacements in porcine functional spinal units exposed to varying impact severities are below ultimate shear failure displacements and does not support a lumbar spine injury mechanism resulting in acute traumatic bone fractures and/or acute traumatic IVD herniations in previously “healthy” tissues. Overall, the small FCL strain magnitudes during impacts and unchanged FCL mechanical properties post-impact suggest that the FCL does not undergo injurious or permanent mechanical changes in response to low to moderate MVC impact scenarios. Collectively, the findings from this thesis indicate that there are no direct mechanical changes that would indicate the high incidence of low back pain reporting following low to moderate severity rear-end motor vehicle impacts. However, changes in passive tissue properties were observed, and if persistent over time, may predispose individuals to secondary pain pathways. It is also important to note that this thesis tested healthy conditions and the results do not directly apply to pre-existing LBP cases being exposed to the same impacts.
History-Dependent Changes to the Structure, Properties, and Function of the Cartilaginous Endplate
(University of Waterloo, 2023-04-12) Zehr, Jackie Doreen; Callaghan, Jack
The performance of manual lifting is associated with 33-51% of incidental low back injuries in work, leisure, and sport/exercise contexts. To effectively prevent low back injuries and evaluate the risk of occurrence, knowledge on the fundamental pathways of microscopic damage accumulation in lumbar spine tissues is required and lacking in the literature. This thesis broadly explored this knowledge gap in the cartilaginous endplate (CEP), which is a hypothesized origin for compression-induced low back injuries and degenerative changes to the intervertebral disc. Therefore, the global objectives of this dissertation included: 1) to quantify the effect of cyclic compression paradigms on the properties and microstructure of the cartilaginous endplate; 2) to examine the effect of cyclic loading parameters on microscopic and macroscopic injury patterns in the cartilaginous endplate; and 3) to characterize the cycle-dependent ultimate compression trajectories in response to acute loading histories. To address these objectives, in vitro mechanical testing and immunofluorescence staining techniques were developed and performed on intact spinal units and isolated CEP tissue. The effects of joint posture, variation in peak compression force, and loading duration on cycle-dependent changes to spinal joint mechanics, isolated CEP properties, and the pathways of microstructural and constitutive damage were quantified. Compared to neutral joint postures, cyclic loading applied to flexed spinal joints reduced the ultimate strength and CEP stiffness at a given loading duration, irrespective of the peak compression variation. An effect of peak compression variation was observed only within neutral postures and beyond the approximate mid-point of the joint lifespan; a 40% variation reduced the joint strength and CEP stiffness compared to the 10% and 20% variation groups. These altered mechanical properties were supported by evidence of sub-surface microstructural void development followed by damage to native type II collagen proteins within the central CEP region. Data obtained from these in vitro mechanical tests were then used to mathematically characterize the relationships between UCT and loading duration. The second-order polynomial functions demonstrated the depreciation of ultimate compression tolerance and altered safety margins for a given loading history. These data collectively highlighted the importance of spinal joint posture for mediating the damage cascade, which can inform the priorities of job (re)design, clinical intervention, and movement training. The morphology of microstructural injury patterns was also driven by joint posture during sub-threshold cyclic loading, and the lesion size generally progressed as a function of loading duration. That is, cartilage microfractures were more common in neutrally positioned joints, while avulsion and node microinjuries were most common in flexed spinal units. However, on a macroscopic level, the failure morphology was less sensitive to posture and was attributed to the pace of damage accumulation in the sub-chondral bone relative to the hyaline cartilage surface. This notion was experimentally demonstrated by imposing targeted trabecular bone strength deficits within intact vertebrae and performing subsequent fatigue testing. Initially healthy spinal joints resulted in fracture lesions, while spinal joints with pre-existing strength deficits resulted in Schmorl’s nodes over 50% of the time. This dissociation of macroscopic injury mechanisms provided new insights into their prevention, treatment, and diagnosis and ultimately improves the specificity of ergonomics tools that are developed from in vitro experimental data. Overall, this research documents the effects of joint posture, variation in peak compression force, and loading duration on the pathways and time-course of microscopic damage in the cartilage endplate of the spine. These data will be used to broadly inform task design, load management, and injury prevention initiatives in many occupational sectors, specifically public protection (i.e., military, emergency response personnel), health care, manufacturing, and professional/colligate sport where low back injuries are a common and costly cause of personal disability and lost work time. The work of this thesis further advanced the methodology used within the broader field of spine biomechanics and the experimental results represent a significant step to understanding the mechanisms and prevention of lifting-related overuse injuries in the lumbar spine.
The Prediction of Nociceptive Neural Activity in Passive Tissues following Lumbar Spine Flexion
(University of Waterloo, 2021-11-26) Viggiani, Daniel; Callaghan, Jack
Low back pain is a costly and debilitating disorder; however, most cases are categorized as being non-specific: low back pain without an identifiable origin or cause. Non-specific low back pain can be broadly considered and treated as either musculoskeletal disorders or pain disorders. In the musculoskeletal case, mechanics and loading history are believed to disrupt or damage tissues in the low back, which then generate nociceptive signals to be interpreted as pain. If the low back pain is a pain disorder, the disruption or damage is not with the tissues of the lower back, but rather the nervous system that transmits or interprets these nociceptive signals. Additionally, these subcategories of non-specific low back pain are not wholly independent since mechanical exposures can influence nervous system activity and vice versa. A specific outcome of this interconnectedness between mechanics and neural encoding is that a mechanical exposure can alter our ability to detect mechanical loads or mechanical sensitivity. One mechanical exposure that is linked to low back pain development and has been documented to alter neural activity is lumbar spine flexion. The purpose of this thesis was to determine the extent and mechanisms underlying how lumbar spine flexion can alter lower back mechanical sensitivity through a combination of viscoelastic creep and muscle activity, and to determine the implications those changes could have on the development of low back pain. The methods undertaken to achieve this thesis’ purpose were a combination of in-vivo human laboratory experiments, ex-vivo benchtop histology and mechanical testing, and in-silico modelling across four studies. Studies 1 and 2 quantified how mechanical sensitivity was altered over time in response to static and repetitive lumbar spine flexion respectively, Study 3 quantified the innervation properties of lumbar spine tissues, and Study 4 simulated mechanical exposures before and after lumbar spine flexion exposures to determine the nociceptive neural activity those exposures and conditions could generate. The first two studies employed a similar design and methodology measuring mechanical sensitivity and biomechanical variables before and up to 40 minutes after a 10-minute lumbar spine flexion exposure. For Study 1, the exposure was a static, seated, maximal lumbar spine flexion exposure and for Study 2, the exposure was a repetitive, standing, maximal lumbar spine flexion exposure. A custom motorized pressure algometer was constructed for these studies and used to track three measures of mechanical sensitivity—pressure-pain threshold, stimulus intensity, and stimulus unpleasantness—in the lower back and tibial shaft. Accelerometry was used in both studies to track the development and recovery from viscoelastic creep through lumbar spine flexion range of motion, and surface electromyography was used to determine flexion-relaxation (mean amplitude) in Study 1, and muscle fatigue (mean power frequency) in Study 2. Isometric joint strength and ratings of perceived exertion were also measured in Study 2. These data were fed into two main statistical processes: the first aimed to determine the time-course of mechanical sensitivity changes in the lower back relative to the tibial control site, and the second was to determine if any of the biomechanical variables (creep, muscle use, strength) or tibial mechanical sensitivities could predict lower back mechanical sensitivity changes. The static exposure generated a 10.3% creep response (4.4 ± 2.7°) in flexion range of motion that lasted for at least 40 minutes after the exposure. This exposure caused a transient increase in lower back stimulus unpleasantness but otherwise did not affect mechanical sensitivity nor did it affect flexion-relaxation. The strongest predictor of lower back mechanical sensitivity throughout the static exposure was the tibial surrogate; however, the magnitude of creep was also a significant predictor of changes in lower back pressure-pain thresholds. Despite being significant, these significant predictors could not explain the majority to the variance in mechanical sensitivity, and these changes appear more related to emotional affect than a physiological response. Study 1 concluded that a static lumbar spine flexion exposure that did not incorporate muscle activity did not alter nociceptive activity but could shape how nociceptive activity is experienced. The repetitive exposure generated a 5.0% creep response (2.7 ± 1.4°) in flexion range of motion dissipated within 5 minutes of the exposure ending. This exposure caused an immediate and transient decrease in lumbar spine extensor mean power frequency (5.1%) and lower back joint strength (9.8%) indicative of muscle fatigue, and a delayed 13.6% increase in lower back pressure-pain thresholds occurring 10 minutes after the exposure ended. Like Study 1, tibial mechanical sensitivities were the strongest predictor of lower back mechanical sensitivities, however interaction terms between these tibial surrogates and either creep magnitude or fatigue indicators (mean power frequency and strength) were also significant predictors. The delayed desensitization following this repetitive exposure was believed to arise from a combination of creep development and muscle use. The third study used lumbar spine tissues harvested from four cadaveric donors to determine the relative concentration of four neural membrane molecules (Protein Gene Product 9.5 (PGP9.5), Calcitonin Gene-Related Peptide, Bradykinin B1-Receptor, and Acid-Sensing Ion Channel 3 (ASIC3)) relevant to detecting mechanical stimuli in three tissues (dermal skin, superficial posterior annulus fibrosus, and the supraspinous-interspinous ligament complex) using Western Blotting. Only PGP9.5 and ASIC3 were found consistently in any of the three tissues. PGP9.5 had similar concentrations in skin and ligament, both of which were at least 12.8 times higher than in annular tissues. ASIC3 was most common in skin, followed by ligament, then annulus fibrosus, however the ratio of ASIC3:PGP9.5 was highest in annular tissue. The fourth study documents a model of nociceptive activity that predicts the likelihood that three exposures (pressure-pain threshold, flexion range of motion, and tissue failure) would generate nociceptive activity in the brainstem given a tissue (skin, annulus, or ligament), a viscoelastic state, ζ(t), and a muscle activity state, ϕ(t). The model simulated a single tissue-exposure combination for a sample of 100 mechanical sensitivities derived from the data in Studies 1 and 2. The model itself consisted of a Sensitivity Module that converted a tissue stress to an electrical current and a Neurological Module that used the electrical current to simulate the behaviour of a network of Hodgkin-Huxley neurons. The pressure-pain threshold exposure was used to validate the model and derive values for ζ(t) and ϕ(t), which were then applied to the other two exposures in annular and ligament tissues. While ζ(t), representing any effects related to creep following lumbar spine flexion, had minimal effects on nociceptive neural activity, ϕ(t), representing muscle activity-related effects of lumbar spine flexion, could inhibit nociceptive activity substantially. A major prediction from the model is that annulus fibrosus failure would be unlikely to generate any nociceptive activity in 12% of the population, and that characteristics of the exposure could increase that percentage to as many as 99.9% depending on the mode of failure. Flexion range of motion consistently generated no nociceptive activity in all tissues and conditions, and ligament failure consistently generated nociceptive activity regardless of other factors. While both viscoelastic creep and muscle activity related to lumbar spine flexion can influence mechanical sensitivity, the effects of muscle activity were more prominent, and could meaningfully influence the connection between tissue disruption and low back pain. These effects were most notable in exposures that have the potential to damage the annulus fibrosus.
The Role of Low Back Capacities on Loaded and Unloaded Functional Movements: Squat and Lunge
(University of Waterloo, 2024-08-29) Zafar, Elizabeth; Callaghan, Jack
Variability of movement patterns across individuals have been well documented in healthy young adults. Large heterogeneity of movement patterns within seemingly homogenous populations suggests the possible presence of subgrouping of individuals. This variability makes it difficult to study and draw conclusions based on group effects, since group means may not be representative of individuals within the group, and especially when subgroups respond differently to interventions. It is also well established that certain movements and movement characteristics are relevant to movement efficiency, tissue exposure, and injury risk, however, it is not fully understood why individuals utilize certain movement patterns over others. It is plausible that physical capacity related differences between subgroups of individuals can help explain differences in movement. As such, this thesis aimed to cluster individuals according to their lumbar movement profiles during functional movements, and then relate characteristic profiles of each subgroup to the low back capacities of strength, muscular endurance, proprioception, and motor control. Additionally, this thesis investigated the effects of introducing a moderate challenge (i.e., loading) to the lumbar movement profiles during functional movements. Thirty-two healthy young adults (16 M, 16 F) performed two sets of ten repetitions each of squat (SQT) and lunge (LNG) in both unloaded (UL) and loaded (LD) conditions. Additionally, lumbar capacity tests of strength (S), endurance (E), joint position accuracy (P-A), joint position sensitivity (P-S), and motor control (MC) were assessed. State spaces of lumbar angle dynamics for each condition of movement were constructed, then discretized into 48 bins and averaged across repetitions. State spaces were then analyzed using spectral clustering with the number of subgroups selected based on the strongest silhouette score. Analyses of variance (ANOVAs) testing the effect of sex and group on each capacity test’s scores were conducted. The results of the clustering produced two groups with weak clustering strength in each condition. In both the SQT UL and SQT LD conditions, a significant interaction between sex and group in P-S (p = 0.01), and a significant effect of sex in E (p = 0.04)were found. In the LNG UL condition, a significant interaction between sex and group in P-A (p = 0.04), and a significant effect of sex in E (p = 0.04) were found. Significant interactions between group and sex were found in both P-S (p = 0.04) and MC (p = 0.03) for the LNG LD condition. Differences in lumbar capacities between groups were related to features of the state spaces, including shape, diffuseness, and intensity of attractors. This thesis highlighted the importance of physical capacities on movement patterns and affirmed the necessity of characterizing subgroups of individuals within a heterogeneous sample population. This thesis provides a framework for more comprehensive investigations into the relationships between specific capacities and movement profiles.

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