A biomechanical study of balance recovery during the fall forward.

The study deals with the biomechanics of balance recovery of human subjects in a falling forward situation. Eight subjects took part in the experiment. The subject, held in the initial leaning forward position, was released without his knowledge. The instruction was to recover the induced disequilibrium by walking. The biomechanical analysis shows two phases in the balance recovery. The first phase--preparation phase--is characterized by three events at fixed timing whatever the initial inclination. (i) Dynamic reaction time, showing no significant inter-individual variation (mean value = 90.8 ms). (ii) Braking of the forward fall, between 184 ms and 237.2 ms, depending on the subject. (iii) Beginning of the swing phase--i.e. toe-off instant--between 235.9 ms and 328.3 ms, depending on the subject. The second phase--gait execution phase--is characterized by the duration of the swing phase, the duration of the stance phase, the stride length and execution speed. The durations diminish whereas the stride length and the execution speed increase with respect to the initial inclination. For the same execution speed, the stride length is shorter than in normal walking. It has been concluded that balance recovery following an induced fall forward begins with an invariable preparation process which is followed by an adaptable recovery one.