Effects of hamstring conditioning contraction on landing biomechanics and surface EMG: a randomized controlled trial

This study aimed to investigate the effects of post-activation potentiation (PAP) of the hamstrings on surface electromyography (sEMG) characteristics and knee joint biomechanics during landing.

This two-arm, parallel-group randomized controlled trial (1:1 allocation) included 34 male collegiate athletes assigned to a PAP group (n = 17) or a control group (n = 17). The PAP group performed a 5-s hamstring MVIC followed by an 8-min interval, whereas the control group remained seated quietly for an equivalent 8-min interval without conditioning contraction. Drop-landing tasks were completed before and after the intervention. Kinematic, kinetic, and sEMG data were collected synchronously. Wavelet decomposition was applied to hamstring sEMG signals across four frequency bands. Primary outcomes were wavelet-derived EMG power in the 60-200 Hz frequency band for the biceps femoris and semitendinosus/semimembranosus during landing; all other EMG bands, biomechanical variables, iEMG, and co-contraction indices were considered secondary/exploratory. Trial registration: Not registered.

For the primary outcomes, the PAP group showed significant pre-post increases in wavelet-derived EMG power within the 60-200 Hz frequency band for both the semitendinosus/semimembranosus and biceps femoris, whereas no significant pre-post changes were observed in the control group. Post-intervention between-group comparisons further showed significantly higher 60-200 Hz wavelet power in the PAP group than in the control group for the semitendinosus/semimembranosus (FDR-adjusted p = 0.014, 95% CI: 2100.466-6465.455) and biceps femoris (FDR-adjusted p = 0.045, 95% CI: 605.924-1131.846). Among secondary and exploratory outcomes, frequency-domain changes were observed in other bands, including increased 200-480 Hz wavelet power in both muscles and decreased 0-20 Hz wavelet power in the biceps femoris. Biomechanically, the PAP group demonstrated greater maximal knee flexion angles (p < 0.001, 95% CI for PAP - Control [6.374, 10.699]) and reduced sagittal- (p = 0.043, 95% CI for PAP - Control [-0.323, -0.010]) and transverse-plane (p = 0.002, 95% CI for PAP - Control [-0.360, -0.068]) knee joint moments compared with the control group, indicating altered joint loading patterns during landing.

Hamstring PAP was associated with acute changes in hamstring surface EMG characteristics a nd landing biomechanics, including increased 60-200 Hz wavelet-derived EMG power, greater knee flexion, and lower frontal- and transverse-plane knee joint moments.