Muscle Co-contractions Worsen In The ACL Reconstructed Limb When Gait Is Challenged Compared To Normal Gait

Abstract

PURPOSE: Greater and more symmetrical IKEM predict better functional outcomes after anterior cruciate ligament reconstruction (ACLR). Challenging walking tasks create greater internal knee extensor moments (IKEM) than normal walking after ACLR. Exploring muscle activity during normal and challenging walking could elucidate the underlying muscle responses to increased knee moments. METHODS: Three females (5-12 months post ACLR) who were cleared to return to sports participated. Subjects first completed normal walking followed by walking with a 50% body weight load while towing a sled and wearing a weighted vest. Order of the loaded conditions was randomized. Muscle activity of the medial and lateral quadriceps and hamstrings was measured bilaterally with surface electrodes (Fig 2). Walking speed was controlled. IKEM impulses and muscle activity while generating an IKEM were calculated during the stance phase of the task. Integrated electromyography (EMG) data were normalized to maximal EMG activity during a voluntary isometric contraction (MVIC). RESULTS: Descriptive statistics demonstrate that IKEM impulses and quadriceps activity increased when challenged (vest and sled) compared to normal walking. (Fig 1 and 2) EMG activity was greater in the ACLR limb across tasks, though the confidence intervals were large. (Fig 2) Though the small sample size was not powered to determine statistical significance, the greater magnitude of co-contraction activity in the ACLR limb was apparent for all females across all walking tasks. CONCLUSION: Quadriceps muscle activity increased along with IKEM impulses as expected. The asymmetrical muscle activity and large magnitude of hamstring activity was not expected. High levels of muscle co-contractions to achieve greater IKEM in the ACLR limb in these females is concerning.