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

Despite repeated demonstration of how balance can be restored with protective 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. The purpose of this study was, therefore, to determine failure rate and the characterization for balance recovery after young adults exposed to an experimentally induced novel slipping perturbation. Twenty-four healthy young adults first performed three to nine trials of regular sit-to-stand. In the following trial, slipping suddenly occurred during the termination of the sit-to-stand when the low-friction platform on which the participant stood was released. Participants were given no prior practice or knowledge of the experiment design. Slipping was then repeated in the subsequent trials. The results demonstrated for the first time that a high percentage (62%) of participants failed to recover standing balance, despite the fact that 14 of these 15 participants had initiated stepping at their first encounter of a sudden slip. Such failure was avoided immediately after the first encounter. It was postulated that a delay in the step initiation might have contributed to substantial vertical descent of the center-of-mass, leading to failure of balance recovery in limb collapse. To verify this and other hypotheses, a shift in experimental paradigms is warranted to include the study of spontaneous protective responses elicited when individuals first encounter previously unfamiliar balance perturbation as in real-life situations.