Effects of an isokinetic fatigue protocol on knee flexion–extension performance and hamstrings-to-quadriceps ratio in women professional soccer players

Knee flexion (KFPT) and knee extension (KEPT) peak torque and hamstring-to-quadriceps ratio (H:Q) are used to estimate injury risk and readiness to return to sport. However, isokinetic assessments are traditionally performed at slow speeds (≤ 60°/s) and non-fatigued state, which may not reflect thigh and knee injury conditions in soccer players. Moreover, there is a lack of studies investigating this topic in women athletes. We investigated the effects of a high-speed isokinetic fatigue protocol on (1) KFPT and KEPT during the test; after the protocol (2) KFPT and KEPT at slow (60°/s) and high-speed (300°/s) and (3) conventional (H:QConv) and functional (H:QFunc) H:Q ratios in 20 (40 legs tested) women professional soccer players. A smaller reduction in concentric KFPT (− 34.94 ± 13.55%) than KEPT (− 40.54 ± 4.24%) occurred during the fatigue protocol (p < 0.01). After the fatigue protocol, decreases in concentric KFPT (60°/s: − 15.22 ± 12.66%; 300°/s: − 18.57 ± 11.31%) and concentric KEPT (60°/s: − 16.41 ± 9.31%; 300°/s: − 17.49 ± 8.13%) and eccentric KFPT (60°/s: − 11.29 ± 12.98%) were observed (p < 0.01). H:QConv showed no alteration after the fatigue protocol, while H:QFunc increased (+11.29 ± 12.98%; p < 0.01). In conclusion, KFPT and KEPT reductions during the fatigue protocol occurred. After the protocol, fatigue affected concentric KFPT and concentric KEPT at slow and high speeds and less eccentric KFPT capacity, and thus resulted in an increased H:QFunc.