Isokinetic eccentric exercise of quadriceps femoris does not affect running economy

The purpose of this study was to investigate whether running economy is affected by isokinetic eccentric exercise designed to cause muscle damage. Twenty-four young healthy men performed 120 maximal voluntary eccentric actions at each thigh's quadriceps muscle at an angular velocity of 60 degrees .s. The participants were then randomly divided into 2 equal groups, 1 of which exercised 24 hours later, while the other group rested. Muscle damage indicators (i.e., serum creatine kinase, delayed onset muscle soreness, and eccentric, concentric, and isometric peak torque) and running economy indicators (i.e., oxygen consumption, pulmonary ventilation, respiratory exchange ratio, respiratory rate, and heart rate during treadmill running at 2.2 and 3.3 m.s) were assessed prior to and 48 hours following the eccentric exercise. All muscle damage indicators changed significantly in both groups (p < 0.05) in a way suggestive of considerable muscle damage. Running economy indicators of the exercise group demonstrated only an elevation of respiratory rate at 48 hours (p < 0.05) and a tendency to lower economy compared to the resting group. It can be concluded that isokinetic eccentric exercise applied to the quadriceps femoris muscles did not affect running economy 48 hours later and that resting during this period tended to result in more economical running compared to exercising at 24 hours.