Background The primary mechanism for hamstring strain injury is high speed running however insults also occur during kicking in which they are more severe.

Objective To examine the effect of 100 drop punt kicks on isokinetic knee flexor strength and surface electromyographic (sEMG) activity of biceps femoris (BF) and medial hamstrings (MH).

Design Randomised control study.

Setting Community level Australian football.

Participants Thirty-six recreational footballers were recruited.

Interventions Participants were randomly assigned to kicking or control groups. Dynamometry was conducted immediately before and after the kicking or 10 minutes of sitting (control).

Main Outcome Measurements Knee flexor strength and biceps femoris and medial hamstring surface electromyography.

Results Eccentric strength declined more in the kicking than the control group (p<0.001; d=1.60), with greater reductions in eccentric than concentric strength after kicking (p=0.001; d=0.92). No significant between group differences in concentric strength change were observed (p=0.089; d=0.60). The decline in normalized eccentric hamstring sEMG (BF and MH combined) was greater in the kicking than the control group (p<0.001; d=1.78), while changes in concentric hamstring sEMG did not differ between groups (p=0.863; d=0.04). Post-kicking reductions in sEMG were greater in eccentric than concentric actions for both BF (p=0.008; d=0.77) and MH (p<0.001; d=1.11). In contrast, the control group exhibited smaller reductions in eccentric than concentric hamstring sEMG for BF (p=0.026; d=0.64) and MH (p=0.032; d=0.53). Reductions in BF sEMG were correlated with eccentric strength decline (R=0.645; p=0.007).

Conclusions Reductions in knee flexor strength and hamstring sEMG are largely limited to eccentric contractions and this should be considered when planning training loads in Australian Football.