Continuous and discrete electromyographic analysis of trunk and hip extensor musculature during the Biering-Sørensen test in athletes with a history of hamstring strain injury.

This study examined electromyography (EMG) responses of trunk and hip extensor muscles during the Biering-Sørensen test in athletes with a history of hamstring strain injury (HSI). 34 athletes with HSI (occurring an average of 6.68 months prior to testing; 28 involving the biceps femoris long head (BFlh), 5 the semitendinosus, and 1 undefined) and 25 uninjured performed the Biering-Sørensen test. EMG signals were recorded from the erector spinae (ES), BFlh, and gluteus maximus (GMax). Group differences in continuous median frequency (MNF) and mean absolute value (MAV) waveforms were analyzed using statistical parametric mapping and slopes and initial values were examined using linear mixed-effects models. The HSI group demonstrated significantly lower endurance scores compared to controls (162.1 ± 64.4 s vs. 192.1 ± 47.4 s; p = 0.036). MNF waveforms did not differ between groups (p > 0.05). The ES normalized MAV values were significantly higher in the HSI group compared to the uninjured group during the initial and terminal phases of the task (p < 0.05). Athletes with HSI exhibited higher initial ES and BFlh MAV than controls as well as a lower GMax MNF slope in the full sample analysis (p = 0.019), although this effect was not confirmed in subgroup analyses. The altered EMG patterns in athletes with HSI history likely contribute to reduced endurance and suggest that rehabilitation should prioritize re-establishing balance contribution across the trunk and hip extensors.