The effects of targeting on the ground reaction forces during level walking

This study evaluated the effect of a 30% perturbation of step length on the ground reaction forces during level walking. The subjects walked across a force platform from which the vertical and anterior-posterior horizontal components were recorded. There were four experimental conditions: normal step length, short step length, long step length, and normal step length without visual cues. The normal step length without visual cues served to test whether there was an effect on the gait variables as a function of walking in the dark without perturbation. Results showed that the absence of light did not affect the ground reaction forces during normal level walking. Both the long and short steps, however, showed significantly altered peak forces during the first half of the stance phase. There were no significant differences in the peak forces during the second half of the stance phase. When subjects target the force platform they modulate their gait style only during the initial weight bearing phase of the cycle. During the second half or propulsive phase the pattern of push off force was as for a normal step. Further, the timing characteristics of the gait appeared to be preserved, suggesting the subjects modulate the forces in order to maintain these timing features.