Heavy-intensity aerobic exercise affects the isokinetic torque and functional but not conventional hamstrings:quadriceps ratios

Running exercises are frequently related to muscular injuries, which may be a result of muscular imbalance. The present study aimed to verify the effects of heavy-intensity continuous running exercise on the functional and conventional hamstrings:quadriceps ratios, and also in the knee flexors and extensors EMG activity in active non-athletic individuals. Sixteen active males performed maximal isokinetic concentric and eccentric knee flexions and extensions at 60°s−1 and 180°s−1. In another session, the same procedure was conducted after a continuous running exercise at 95% onset of blood lactate accumulation. Torque and electromyographic ratios were calculated from peak torque and integrated electromyographic activity (knee flexor and extensors). Creatine kinase was measured before and 24h after running exercise. Eccentric torque (knee flexion and extension) decreased significantly after running only at 180°s−1 (p<0.05). No differences were found for the conventional torque ratios (p>0.05), however, the functional torque ratios at 180°s−1 decreased significantly after running (p<0.05). No effects on the electromyographic activity and electromyographic ratios were found (p>0.05). Creatine kinase increased slightly 24h after running (p<0.05). Heavy-intensity continuous running exercise decreased knee flexor and extensor eccentric torque, and functional torque ratios under fast velocities (180°s−1), probably as result of peripheral fatigue.