Investigating the Impact of External Passive Compression on Central and Peripheral Hemodynamics
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The use of passive compression has been extended from a clinical treatment to an elective tool used by healthy individuals in an attempt to improve exercise performance. The rationale being that graduated compression socks would enhance the capabilities of the muscle pump and therefore increase venous return to the heart, leading to increased cardiac efficiency and better exercise performance. There is currently conflicting evidence regarding the effectiveness of graduated compression socks on improving central and peripheral hemodynamics in a healthy population. These conflicting results are believed to be due to varying test protocols (e.g., type of exercise, duration, and intensity), difference in study populations (e.g., normal participants vs. highly trained athletes), and the variation in the reported strength of the applied pressure (i.e., only reporting the manufacturer’s operating pressure). All of these factors make it difficult to draw concrete conclusions on the effect of compression during exercise and recovery. The goal of this study was to complete a set of controlled experiments to assess the effectiveness of passive compression in healthy subjects and whether they are beneficial for enhancing performance and recovery. The purpose being to compare the results to the discrepancies found in current literature when evaluating external compression in healthy subjects. The scope involved testing 12 healthy individuals who ranged in fitness levels during a simple exercise task while monitoring central and peripheral variables. The experimental protocol involved a three minute baseline period, followed by plantar flexion exercises for five minutes at a rate of 20 raises per minute, and finished with a five minute recovery time. The protocol was repeated twice to investigate the physiological response with and without graduated compression socks. Subjects completed testing on two days, with at least 48 hours between tests, to determine the repeatability of the results. Specific central variables investigated included heart rate, systolic blood pressure, diastolic blood pressure, and cardiac output. Peripherally, popliteal arterial blood velocity, popliteal arterial blood flow, popliteal artery diameter, muscle activity, muscle oxygenation, and the change in pressure from the ankle to knee due to the compression sock were measured. The results indicated that there were no changes in the central hemodynamics with the addition of the socks. At the peripheral level, there were no significant changes in popliteal artery diameter, mean popliteal arterial blood velocity, or mean popliteal arterial blood flow during any of the testing conditions. During exercise, there was an indication that the subjects who experienced an increase in mean popliteal arterial blood velocity or mean popliteal arterial blood flow with the graduated compression socks behaved more consistently than those who experienced a decrease, as implied by lower standard deviation values. The exercise task did not cause any lasting effects on vasculature as there was no significant difference between the popliteal artery diameter values for baseline and recovery and the subjects experienced the same response (i.e., increase or decrease) with the socks during both baseline and recovery. For muscle oxygenation, results indicated a decrease in blood volume in the leg with the graduated compression socks, and a trend towards increased muscle oxygenation and oxygen extraction during exercise. For recovery, there was a trend towards a lower blood volume in the leg with the graduated compression socks implying that even post exercise the socks were working to prevent pooling in the leg. For muscle activity, the same muscle activation was required with and without the socks to complete the test. The height at which the plantar flexion task was completed was tied to lifestyle, those subjects reporting irregular exercise, completed the calf raise exercise at lower heights than those who reported frequent exercise. Furthermore, the locally applied pressure was found to vary dynamically during exercise and then return to baseline values during recovery. Moreover, the strength of the pressure change on the leg from ankle to knee was not correlated to the response of the subject for any of the investigated variables. Finally, no significant differences were found in the immediate hemodynamic recovery time with the addition of the sock. The results found in this study were comparable to other studies investigating the effect of graduated compression socks on hemodynamics. It is not surprising that there were no changes in central hemodynamics, as the external pressure was applied in such a small, localized region. It is also not unexpected that a healthy study population did not lead to significant changes in vascular diameter or blood velocity since the subjects do not suffer from venous deficiencies. The key findings of this study are that the graduated compression socks were beneficial in decreasing blood volume in the leg, as expected with their prescribed function, and have the potential to increase oxygen extraction in a healthy population. Furthermore, the discovery that the local applied pressure varied during exercise should be taken into consideration when utilizing compression socks for various exercise tasks. Finally, this study highlights the importance of control and reporting all aspects of the experimental protocol and data analysis in order to obtain high fidelity results that can be entered, with confidence, into the debate of the effectiveness of graduated compression socks on athletic performance.