Stance phase knee and ankle kinematics and kinetics during level and downhill running.

To study possible mechanisms for muscle soreness in downhill running, ground reaction force and kinematic data were collected on seven male runners during 4.5 m.s-1 level running (LR) and 8.3% downhill grade running (DR). For DR, a force platform was mounted on a sloped concrete block flush with the surface of a ramp. A two-dimensional link segment model was used to calculate net stance phase moments for the knee and ankle. Data were averaged over all subjects for each condition. There was no significant difference (P less than 0.05) between DR and LR for peak flexion velocity, peak extensor moment, or peak power absorption at the knee. Negative work done on the extensor muscles of the knee during stance was significantly greater for DR (58.0 +/- 13 J) than for LR (30.0 +/- 9.0 J). Peak ankle power absorption was significantly greater for DR (619 +/- 85 W) than for LR (396 +/- 180 W). The negative work done on the extensor muscles of the ankle during stance was significantly greater for DR (26.1 +/- 3.2 J) than for LR (12.6 +/- 6.6 J). The results suggest that muscle soreness during DR may be related to high peak power absorption values since the peak joint extensor moments are similar between conditions.