The recovery response to a novel unannounced laboratory-induced slip: The “first trial effect” in older adults

Abstract

Background After a single slip, older adults rapidly make adaptive changes to avoid or eliminate further backward loss of balance or a fall. This rapid adaptation has been termed the “single trial effect”. The purpose of this study was to explore the relationship between the motor errors subjects experienced upon a novel slip and the selection and execution of corrective response by which they modified their ongoing gait pattern and turned it into a protective step. Methods A forward slip was induced in the laboratory among 145 community-living older (≥65 year old) adults who were protected by an overhead full body harness system. An eight-camera motion analysis system recorded subjects’ kinematics, which was used to compute their instability (motor error), recovery step placement (response selection), and stability gain (motor correction). Findings A linear relationship was found between the stability errors at recovery foot liftoff and the distance between the recovery foot and slipping foot at the time of its touchdown, reflecting an appropriate selection of response that was proportionate to the motor error. A linear relationship was also found between this step modification and resulting stability gain, indicating that greater step modification resulted in greater stability gain. This learning behavior was surprisingly consistent regardless whether the outcome was a recovery or a fall. Interpretations These results suggest that fallers and non-fallers all have an intact motor learning foundation that has enabled them to rapidly improve their stability in subsequent exposures.

Neuromuscular mechanisms of motor adaptation to repeated gait-slip perturbations in older adults

“…This study only used one trial for analyzing the novel slip response compared to three trials each for the early and late phase. This was done as it is widely known that a single slip trial exposure is sufficient to induce adaptive changes – known as the first-trial effect 23 , 33 . Thus, using an average of the first three trials would contaminate the true novel slip response.…”

“…It is widely known that a single slip trial exposure is sufficient to induce changes in reactive balance, which is known as the first-trial effect 23 , 33 . After a single slip exposure, individuals show significant improvements in stability and a reduction in the slip distance on the second slip, even though a majority (> 80%) still lose their balance 11 .…”

“…Due to the fast adaptation in kinematic outcomes to slip perturbations, changes in neuromuscular control could also occur after very few slips 23 . Therefore, only the first slip trial was used for muscle synergy extraction for the novel condition.…”

Mobile Brain Imaging to Examine Task-Related Cortical Correlates of Reactive Balance: A Systematic Review

“…Secondly, multicomponent PEPs provide an instantaneous snapshot of cortical changes related to reactive balance tasks; however, a majority of studies have used average trial analysis to quantify them. Previous neurophysiological studies have indicated that perturbation-induced motor adaptation can occur in as little as a single trial in healthy young and older adults [ 104 , 105 , 106 ]. Hence, future studies should test the feasibility and robustness of using single-trial PEP analysis.…”

Severity of Unconstrained Simultaneous Bilateral Slips: The Impact of Frontal Plane Feet Velocities Relative to the Center of Mass to Classify Slip-Related Falls and Recoveries

“…However, friction is likely to stay linear as we previously tested static coefficient of friction of the WASP under a range of simulated body weights and it did not change ( 7 ). Learning effects may arise after exposure to the first slip despite being exposed to different types of slip onset phases during stance, hence this could be a limiting factor, especially since literature reported biomechanical and motor adaptation after a single exposure to sagittal induced ( 54 , 55 ) and unconstrained induced ( 56 ) in-lab slips. The previously mentioned studies did not report the exact resting period between each slip trial, and despite the resting period (5-min) was controlled in this study, it is uncertain if such resting period is sufficient to exclude proactive adaptation.…”