Influence of prolonged intermittent high-intensity exercise on knee flexor strength in male and female soccer players

This study investigated the effect of an acute, prolonged, intermittent, high-intensity single-leg pedalling exercise task (PIHIET) on the isokinetic leg strength of the knee flexors in six male and seven female collegiate soccer players. Following determination of single-leg V̇O_2peak, subjects completed a PIHIET designed to simulate the energetics of soccer match play (~90 min in total; ~70% single-leg V̇O_2peak). Pre-, mid- and post-PIHIET gravity-corrected indices of knee flexion peak torque (PT) and range of motion-relativised torque at 15% of knee flexion (RRT_15%; 0% = full knee extension) were assessed at a lever-arm angular velocity of 1.05 rad·s⁻¹ for intervention and control limbs using an isokinetic dynamometer. Repeated measures ANOVAs revealed significant condition (PIHIET, control) × time (pre-, mid-, post-PIHIET) interactions for knee flexion PT (F _[2,22]=26.2; P<0.001) and RRT_15% (F _[2,22]=20.1; P<0.001). Flexion PT and RRT_15% were observed to decrease, pre- to post-intervention, from 92.8 (28.7) N·m to 72.1 (28.0) N·m and from 63.8 (17.5) N·m to 47.9 (18.4) N·m respectively, for the intervention limb alone. These data corresponded to 22.3% and 24.9% mean reductions pre–post intervention in PT and RRT_15%. Exploratory post hoc analysis of the pattern of the relative deterioration (%) of PT and RRT_15%, for the intervention limb alone, revealed a three-way interaction [group (male, female) x parameter (PT, RRT_15%) x assessment phase (pre- to mid-PIHIET, mid- to post-PIHIET)] (F _1,11=5.2; P<0.05). This interaction characterised a greater deterioration of strength performance during the mid- to post-PIHIET assessment phase, at the extremes of range of motion (RRT_15%) for the female group. The greater percentage of mid–post phase strength loss observed in women near the end-range extension may potentially be implicated in the higher incidence of knee injury reported in female soccer players.