Hamstring-to-quadriceps fatigue ratio offers new and different muscle function information than the conventional non-fatigued ratio.

ABSTRACT

Commonly used injury risk prediction tests such as the hamstring-to-quadriceps (HQ) strength ratio appear to be poor predictors of non-contact injury. However, these tests are typically performed in a non-fatigued state, despite accumulated fatigue being an important risk factor for both hamstring strain (HS) and anterior cruciate ligament (ACL) injuries in professional soccer players. After the effect of different HQ calculation methods were compared and contrasted, the influence of neuromuscular fatigue on the HQ strength ratio and the association between fatigued and non-fatigued ratio scores were examined. Thirty-five professional soccer players performed a 30-repetition isokinetic fatigue test protocol. Peak knee joint moments were computed for each repetition, and the HQ conventional ratio (HQCR ) was calculated using several different, previously published, methods. Knee extensor and flexor moments were statistically decreased by the sixth repetition and continued to decrease until the end of the protocol. However, the HQ ratio was statistically decreased at the end of the test due to a significant reduction in knee flexor moment (correlation between change in knee flexor moment and change in HQ, r≈.80; P<.01). Moreover, HQ measured in fatigue (ie, HQFatigue ) at the end of the test was greater than HQCR (1.25-1.38 vs 0.70, P<.01), these variables were weakly correlated (r=.39, P=.02), and subject rankings within the cohort based on HQCR and HQFatigue were different (rs =0.25, P=.15). The present data suggest that HQ ratio measurement during a fatiguing test (HQFatigue ) provides different outcomes to the traditional HQCR . The observed significant hamstring fatigue and the difference, and weak correlation, between HQCR and HQFatigue indicate that useful information might be obtained with respect to the prediction of HS and ACL injury risk. The potential predictive value of HQFatigue warrants validation in future prospective trials.