The effect of muscle fatigue on knee flexor to extensor torque ratios and knee dynamic stability

Muscle fatigue is a problem that patients and athletes frequently encounter. The knee joint stability is very important for these groups. There are several ways for evaluating knee joint stability. One of these ways is determining hamstring and quadriceps strength ratios. Such ratios consisting of functional ratio and conventional ratio are indicated as predispositions to injury. These ratios, in particular functional ratios, are estimated as coactivation of hamstring and quadriceps muscles. It is considered that muscle fatigue affects these ratios. Thus the purpose of this research was to investigate whether hamstring and quadriceps muscle fatigue has any effect on the ratios and knee dynamic stability? Thirty-two normal male amateur football players participated in this study. All tests were performed in the sitting position, 10 to 90 degrees on knee motion and 120 degree per second angular velocity by dynamometer isokinetic Biodex System 3. Peak torque and average peak torque were recorded. In the fatigue protocol, they reciprocally and concentrically extended and flexed knee until quadriceps peak torque declined up to 50%. Prefatigue and post fatigue functional and conventional ratios were compared using the paired mest. The results showed that there were no significant differences between prefatigue and post fatigue tests. It can be concluded that these ratios as well as coactivation of muscles remain oF constant after fatigue. This could be a mechanism for unchanging knee dynamic stability.