Induced limb collapse in a sudden slip during termination of sit-to-stand

Despite repeated demonstration of how balance can be restored with protecti ve stepping after the initiation of an induced fall, little is known about how accidental falling to the ground with the participant's body resting in a non-standing posture can be avoided during balance recovery. This is due to the difficulties inherent in experimentally eliciting such an event. Th e purpose of this study was, therefore, to determine failure rate and the c haracterization for balance recovery after young adults exposed to an exper imentally induced novel slipping perturbation. Twenty-four healthy young ad ults first performed three to nine trials of regular sit-to-stand. In the f ollowing trial, slipping suddenly occurred during the termination of the si t-to-stand when the low-friction platform on which the participant stood wa s released. Participants were given no prior practice or knowledge of the e xperiment design. Slipping was then repeated in the subsequent trials. The results demonstrated for the first time that a high percentage (62%) of par ticipants failed to recover standing balance, despite the fact that 14 of t hese 15 participants had initiated stepping at their first encounter of a s udden slip. Such failure was avoided immediately after the first encounter. It was postulated that a delay in the step initiation might have contribut ed to substantial vertical descent of the center-of-mass, leading to failur e of balance recovery in limb collapse. To verify this and other hypotheses , a shift in experimental paradigms is warranted to include the study of sp ontaneous protective responses elicited when individuals first encounter pr eviously unfamiliar balance perturbation as in real-life situations. (C) 19 99 Elsevier Science Ltd. All rights reserved.