EMG measurement of the adductor muscles during walking and running
Introduction Increased pelvic drop has been linked to a range of musculoskeletal running injuries and may be linked to atypical activation pattern of the muscles surrounding the pelvis. However, to date, previous research investigating pelvic drop has focused on the abductor group, with minimal focus on the adductor group. Importantly, the over-activation of the adductor muscles could increase the adduction movement at the hip and therefore increase pelvic drop. However, this has not yet been investigated. Therefore, the studies within this thesis aimed to develop a valid and reliable protocol for measuring the activity of the adductor muscles and to investigate the association between adductor activation patterns and pelvic drop. Methods Ethical approvals were obtained from the University of Salford. Study 1 quantified the relative movement of the adductor muscles under the skin at different hip joint angles and during incremental isometric contraction. In addition, it explored the relationship between adductor torque and the corresponding EMG amplitudes during ramped isometric contraction in 10 participants. Study 2 investigated the between-day reliability for EMG measurements for the adductor muscles collected during both walking and running in 10 healthy runners. Study 3 described the EMG profile and the inter-subject variability for the adductor muscles during running in 25 runners. Study 4 investigated the association between the frontal pelvic plane movement and the adductor activation pattern during the early stance phase of running in 25 runners. Results The results of Study 1 suggested that placing the surface electrodes centrally over the adductor muscles ensure that the adductor muscles remain within the EMG electrode detection volume. Study 2 showed good to high between days reliability in both walking and running for the EMG that was developed for measuring adductor muscles activity. Study 3 suggested that the adductor magnus and gracilis muscles activate at the foot strike while the adductor longus activates at toe off. Study 4 showed that there was a significant strong positive correlation between the degree of adductor magnus activity and the pelvic drop angle. Conclusions The thesis establishes a robust and reliable method for measuring the activity of the adductor muscles using surface EMG electrodes in walking and running. Importantly, runners who exhibit increased pelvic drop also appear to demonstrate increased activity of adductor magnus during early stance phase. This finding motivates future clinical trials which could focus on muscle coordination retraining in order to improve kinematic patterns which have been linked to running-related injuries.
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