Foot rotation influences the activity of medial and lateral hamstrings during conventional rehabilitation exercises in patients following anterior cruciate ligament reconstruction

Abstract

Objectives: To investigate the influence of internal and external foot rotation on medial and lateral hamstring electromyographic (EMG) activity during conventional hamstring exercises in patients following anterior cruciate ligament (ACL) reconstruction.

Design: Cross-sectional study.

Setting: EMG activity of medial and lateral hamstrings was recorded during prone leg curl, single-leg bridge and Nordic hamstring exercises with three different foot positions (neutral, internal rotation, external rotation), randomly presented.

Participants: Twenty patients 9-15 months after ACL reconstruction with the semitendinosus-gracilis graft.

Main outcome measures: Concentric and eccentric EMG activity normalized to the EMG activity recorded during a maximal voluntary contraction (MVC).

Results: Compared to the neutral position, the EMG activity of the medial hamstring during prone leg curl exercise was significantly increased by internal foot rotation (concentric: +8.7% MVC; eccentric: +5.9% MVC; p < 0.01; d = 0.88-0.99) and decreased by external rotation (concentric: 5.8% MVC; eccentric: 5.2% MVC; p < 0.05; d = 0.67-0.92). Foot position did not significantly affect hamstring EMG activity during single-leg bridge and Nordic hamstring exercises.

Conclusions: Active internal rotation of the foot during prone leg curl exercise can help selectively maximize muscle activity of the medial hamstring portion. This may have implications for post-operative rehabilitation of ACL patients with a semitendinosus-gracilis graft.

Keywords: ACL reconstruction; Foot rotation; Hamstring; Muscle activity.