Effect of age on the ability to recover from a single unexpected underfoot perturbation during gait: Kinematic responses

•We investigated the age effect in responses to an unexpected underfoot perturbation.•Healthy young altered at the first and up to the fourth recovery step kinematics.•Healthy old kept unchanged in the first recovery step kinematics.•Healthy old changed trunk angle and lateral pelvic movement during the perturbation.•Healthy young did not change frontal body kinematics during the first recovery step.

A sudden underfoot perturbation can present a serious threat to balance during gait, but little is known about how humans recover from such perturbations or whether their response is affected by age. We tested the hypothesis that age would not affect the stepping responses to a nominal 10 degree inversion or eversion of the stance foot during gait. Twenty-three healthy young (22.7 ± 3.35 yrs) and 18 healthy old adults (68.0 ± 7.19 yrs) performed 60 walking trials along a 6-m level walkway at a normal gait speed. In 16 of these trials, a single medial (MP) or lateral (LP) perturbation was randomly administered once under the left or right foot. Recovery step width (SW), step length (SL), trunk kinematics and walking speed were measured optoelectronically. Repeated-measures analysis of variance and post hoc t-tests were used to test the hypotheses. The results show that a MP or LP altered the recovery SL (p = 0.005) and age affected the number of recovery steps (p = 0.017), as well as the first recovery SW and SL (p = 0.013 and p = 0.031, respectively). Both MP and LP caused young adults to have wider SW (p < 0.02) and shorter SL (p < 0.005) without changing trunk movement during their first recovery step. Older adults, however, significantly changed lateral trunk inclination during the first recovery step, decreased their fourth recovery SL (p < 0.001). We conclude that young adults adjust the step kinematics of as many as four recovery steps following this perturbation, a response that was delayed and significantly weaker in older adults who instead exhibited an immediate torso inclination consistent with a hip response strategy.