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

Knee flexion (KF_PT) and knee extension (KE_PT) 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) KF_PT and KE_PT during the test; after the protocol (2) KF_PT and KE_PT at slow (60°/s) and high-speed (300°/s) and (3) conventional (H:Q_Conv) and functional (H:Q_Func) H:Q ratios in 20 (40 legs tested) women professional soccer players. A smaller reduction in concentric KF_PT (− 34.94 ± 13.55%) than KE_PT (− 40.54 ± 4.24%) occurred during the fatigue protocol (p < 0.01). After the fatigue protocol, decreases in concentric KF_PT (60°/s: − 15.22 ± 12.66%; 300°/s: − 18.57 ± 11.31%) and concentric KE_PT (60°/s: − 16.41 ± 9.31%; 300°/s: − 17.49 ± 8.13%) and eccentric KF_PT (60°/s: − 11.29 ± 12.98%) were observed (p < 0.01). H:Q_Conv showed no alteration after the fatigue protocol, while H:Q_Func increased (+11.29 ± 12.98%; p < 0.01). In conclusion, KF_PT and KE_PT reductions during the fatigue protocol occurred. After the protocol, fatigue affected concentric KF_PT and concentric KE_PT at slow and high speeds and less eccentric KF_PT capacity, and thus resulted in an increased H:Q_Func.