The effect of aging on movement characteristics and postural control during stooping and crouching tasks
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Stooping and crouching (SC) postures are integral to many daily tasks, such as retrieving objects from the floor and reaching to low shelves, yet nearly one in four community-dwelling older adults (24%) report having difficulty or being completely unable to perform SC movements. While limited research has identified physical (e.g., lower extremity strength and joint immobility) and behavioural (e.g., obesity and balance confidence) determinants of SC difficulty, little is known about how aging affects the manner in which SC tasks are performed. The objective of this thesis was to describe age-related differences in movement kinematics and balance control during stooping and crouching tasks. Healthy younger (n = 12) and older (n = 12) participants performed a series of object-retrieval tasks – varying in initial lift height, precision required, and duration – that required them to bend over or reach toward the floor. In addition to kinematic and postural control measures describing the movements, measures of lower limb isometric strength, passive range of motion (ROM), and balance confidence were obtained for each participant. Compared to younger, older participants moved slower into and out of self-selected postures, which were characterized by higher whole-body centre of mass (COM) vertical positions. Specifically, older adults exhibited lower vertical COM linear velocities and lower hip, knee, and ankle joint angular velocities during transitions, and higher COM heights achieved through comparatively less flexion in the hip, knee, and ankle joints during object retrieval. Older participants also displayed smaller, more centralized anterior-posterior (AP) COM excursions and lower COM velocities, but higher centre of pressure (COP) activity compared to younger participants, demonstrated through increased COP velocity (relative to COM velocity) and more frequent COP adjustments aimed at regulating COM position. Changing task constraints (i.e., lower initial lift height or longer duration) elicited greater postural changes in younger compared to older participants, potentially reflecting a diminished ability in older adults to make appropriate task-specific adaptations. In particular, younger participants were 4 times more likely than older participants to use a lower to the floor, forefoot crouching posture, especially during longer duration tasks. Older participants also had decreased leg strength and less passive range of motion compared to younger participants. Overall, the results of this thesis demonstrate that despite moving slower through shorter distances, older adults displayed higher COP activity, which may have reflected a heightened effort to control COM position, during SC tasks. This compliments existing works describing age-related differences in movement strategies and balance control during lifting and sit-to-stand tasks. Further work exploring relationships between specific physiological and behavioural factors and SC task performance measures is needed to inform therapeutic intervention strategies.