Mechanisms of adaptation from a multiple to a single step recovery strategy following repeated exposure to forward loss of balance in older adults

摘要

When released from an initial, static, forward lean angle and instructed to recover with a single step, some older adults areable to meet the task requirements, whereas others either stumble or fall. The purpose of the present study was to use theconcept of margin of stability (MoS) to investigate balance recovery responses in the anterior-posterior direction exhibitedby older single steppers, multiple steppers and those that are able to adapt from multiple to single steps following exposureto repeated forward loss of balance. One hundred and fifty-one healthy, community dwelling, older adults, aged 65–80years, participated in the study. Participants performed four trials of the balance recovery task from each of three initial leanangles. Balance recovery responses in the anterior-posterior direction were quantified at three events; cable release (CR),toe-off (TO) and foot contact (FC), for trials performed at the intermediate lean angle. MoS was computed as the anteriorposteriordistance between the forward boundary of the Base of Support (BoS) and the vertical projection of the velocityadjusted centre of mass position (XCoM). Approximately one-third of participants adapted from a multiple to a single steprecovery strategy following repeated exposure to the task. MoS at FC for the single and multiple step trials in the adaptationgroup were intermediate between the exclusively single step group and the exclusively multiple step group, with the singlestep trials having a significant, 3.7 times higher MoS at FC than the multiple step trials. Consistent with differences betweensingle and multiple steppers, adaptation from multiple to single steps was attributed to an increased BoS at FC, a reducedXCoM at FC and an increased rate of BoS displacement from TO to FC. Adaptations occurred within a single test session andsuggest older adults that are close to the threshold of successful recovery can rapidly improve dynamic stability followingrepeated exposure to a forward loss of balance.