Mixed slip-trip perturbation training for improving reactive responses in people with chronic stroke.

This study determined the effect of mixed (slip- and trip-like stance perturbation) training on reactive responses in people with chronic stroke (PwCS) and examined modulation of their reactive responses on higher intensity perturbations posttraining (scaling). Twelve PwCS were exposed to consecutive blocks of treadmill-based slip-like and trip-like perturbations and mixed-stance perturbations. A higher intensity trial was provided postblock and postmixed training. Postural stability [center-of-mass position (CoMP) and velocity (CoMV)], compensatory step length, step count, and trunk angle were examined. PwCS demonstrated an anterior positioning of the CoM, increased step length, and reduced compensatory step count with slip-like block training ( < 0.05). Trip-like block training resulted in reductions in step count, step length, and trunk angle ( < 0.05); however, CoMP remained unchanged ( > 0.05). With mixed training, there was a decrease rather than an increase in step length for slip-like perturbations but a continued decrease in step length and trunk angle was seen on trip-like perturbations ( < 0.05); however, CoMP and step count remained unchanged for both. For both perturbations, the higher intensity trials demonstrated no change from the last block trial. Postmixed block, the higher intensity trial demonstrated an increase only in step count on trip-like perturbation. Between postblock and postmixed higher intensity trials, an increase in step count and decrease in step length was noted only for slip-like perturbations. Block training with slip- and trip-like stance perturbations can enhance reactive responses among PwCS. Although mixed perturbation training continued to improve trip-induced adaptation, prior slip-induced adaptive changes were not maintained and further slip-adaptation was not seen. PwCS demonstrated partial scaling of reactive responses postblock and postmixed training. Block perturbation training led to development of favorable reactive responses to counteract treadmill-based, slip-like and trip-like stance perturbations among people with chronic stroke. During mixed block, previously acquired adaptive changes in reactive responses from slip-block training were not maintained, probably due to interference offered by trip block. Instead, on trip-like perturbations, trip block-induced adaptation was maintained and continued to show further improvement. Our findings might provide future direction for designing effective mixed perturbation training paradigms to counteract both opposing perturbation types.