Do Activation Amplitudes of the Biceps Femoris Long head, Gluteus Medius, Adductor Magnus, and Medial Gastrocnemius Differ during High-speed Treadmill Running after Hamstring Strain Injury in Footballers?

Abstract

Background: Hamstring strain injury is common, recurrent, increasing and costly in running-based sports. However, evidence on adjacent lower-limb muscle activation during high-speed running after injury is limited and inconsistent. Aim: To assess neuromuscular differences during high-speed running in athletes with and without prior hamstring strain injury. Methods: Thirty-one male footballers with (n = 20) and without (n = 11) prior hamstring strain injury ran on a treadmill at 20 km·h⁻¹. Normalised Surface electromyography from the biceps femoris long head, gluteus medius, adductor magnus and medial gastrocnemius was analysed with within-participant and between-group comparisons. We repeated all comparisons after outlier exclusion. Results: No significant within-participant or between-group differences were observed (p ≥ 0.07). After outlier exclusion, medial gastrocnemius, gluteus medius and adductor magnus remained non-significant (p ≥ 0.27). However, the biceps femoris long head exhibited lower activation in the injured compared to the healthy (p = 0.03), with a medium effect size (0.34). Conclusions: During high-speed running, normalised electromyography amplitudes were similar between injured and uninjured/healthy limbs. A potential biceps femoris long head deficit emerged only after excluding statistical outliers. More comprehensive and well-designed studies that include female athletes and utilise standardised normalisation methods are necessary.