Retention of the "first-trial effect" in gait-slip among community-living older adults

Abstract

"First-trial effect" characterizes the rapid adaptive behavior that changes the performance outcome (from fall to non-fall) after merely a single exposure to postural disturbance. The purpose of this study was to investigate how long the first-trial effect could last. Seventy-five (≥ 65 years) community-dwelling older adults, who were protected by an overhead full body harness system, were retested for a single slip 6-12 months after their initial exposure to a single gait-slip. Subjects' body kinematics that was used to compute their proactive (feedforward) and reactive (feedback) control of stability was recorded by an eight-camera motion analysis system. We found the laboratory falls of subjects on their retest slip were significantly lower than that on the novel initial slip, and the reactive stability of these subjects was also significantly improved. However, the proactive stability of subjects remains unchanged between their initial slip and retest slip. The fall rates and stability control had no difference among the 6-, 9-, and 12-month retest groups, which indicated a maximum retention on 12 months after a single slip in the laboratory. These results highlighted the importance of the "first-trial effect" and suggested that perturbation training is effective for fall prevention, with lower trial doses for a long period (up to 1 year). Therefore, single slip training might benefit those older adults who could not tolerate larger doses in reality.

Keywords: Adaptive control; Motor memory; Perturbation training; Stability.

Fig. 1

Schematic of the three-stage, sequential, initial-retest design and protocol. The gait-slip design consisted of a single slip, which was unannounced

Fig. 2

The overground walkway with embedded movable platforms. The simulated slip was triggered by the release of two side-by-side low-friction moveable platforms

Fig. 3

a Reduction in laboratory falls (%) and the retention in b proactive and c reactive control of stability. Measurements were taken from the novel slip (S1, filled squares) of the initial session and the retest slip, which took place 6 months (SR_6, diagonal squares), 9 months (SR_9, open squares), or 12 months (SR_12, dotted squares) after the initial session. For S1, the values were pooled from all three cohorts. *p < 0.05; ***p < 0.001

Fig. 4

Comparisons of the proactive and reactive a knee angle, b maximum BOS velocity, c relative COM position, d relative COM velocity, e step length, and f stability during the first and retest slips for all three cohorts. Knee joint angle was the one formed by thigh segment and the extension line of leg segment with flexion as positive. The knee angle was calculated for the leading leg. The step length was defined by the distance between left and right heels normalized by the body height with the forward direction as positive. *p < 0.05; ***p < 0.001

Fig. 5

a Laboratory falls (%), b proactive stability, and c reactive stability during the novel slip and retest slip for single slip group (open squares) and 24 slips group (open circles). The scale in c is five times of the scale in b. *p < 0.05; ***p < 0.001