The effects of a prolonged running exercise on strength characteristics

The aim of this study was to examine concentric, isometric, and eccentric s trength reductions in the quadriceps muscle following a prolonged running e xercise. Before and after a 2h run (28.4 +/- 1.4 km) peak torque (PT) of th e knee extensors at angular velocities of -120, -90, -60, 0, 60, 120, 180, 240 degrees.s(-1) using an isokinetic dynamometer, electromyographic (EMG) activity of the vastus lateralis (VL) and vastus medialis (VM) muscles and height of a counter movement jump were recorded in twelve well-trained tria thletes. Counter movement jump performances decreased by 10% and PT values were all significantly lower (p < 0.01) at each angular velocity following the run. The torque loss was significantly (p < 0.01) greater under eccentr ic contractions (from 18 to 21 %) than under concentric ones (from 11 to 14 %). EMG activity (RMS) was lower in both VL and VM muscles after the 2h ru n but no difference existed in RMS losses between concentric and eccentric contractions. The present results demonstrate that 1) a prolonged running e xercise more greatly affects eccentric force production in the quadriceps m uscle, and 2) this specificity seems to be due to an impairment of the musc ular contractile mechanism rather than a modification to the neural input.