Time-domain analysis of foot-ground reaction forces in negotiating obstacles.

In recent years there has been increasing interest in the kinetic and kinematic characteristics of adaptations to obstacles and the contribution of these measures to understanding processes of gait control. This study investigated the lead and trail foot kinetic characteristics of unobstructed walking and stepping over obstacles for unimpaired, healthy adult males (n=6) and females (n=6). Two strain-gauged force platforms were employed during free-speed ambulation and stepping over obstacles adjusted to 10, 20 and 30% of leg length. In stepping over obstacles subjects increased obstacle-crossing step lengths and reduced obstacle-crossing speed as a function of obstacle height. The force-time data revealed that, compared with the lead foot, the trail foot generated greater vertical and anterior-posterior force during the push-off/propulsive phase across all obstacle conditions, had lower vertical peak force during mid-stance and produced greater vertical and anterior posterior impulses. While maximum propulsive force increased with obstacle height, its timing in the normalized step cycle was uninfluenced by height. Collectively, the results showed that the constraints of stepping over obstacles imposed different kinetic demands on the lead and trail foot; this is reflected in a complex interaction of braking and propulsive forces. Regulation of the step in this task was not mediated by a single parameter, such as vertical impulse. Copyright 1997 Elsevier Science B.V.