Quantification of reactive arm responses to a slip perturbation

The purpose of this study was two-fold: 1) characterize bilateral upper extremity responses during a slip event in both the sagittal and frontal planes, and 2) to examine the utility of using slip onset as the measurement reference for behavioral responses of the upper extremities using EMG latency. Sixteen healthy young adults were exposed to an unexpected slip during walking. Three-dimensional arm kinematics (excursions) and electromyographic onset latencies (bilateral deltoids) were quantified. Thirteen of the 16 participants recovered their balance following the slip perturbation. Of those who recovered, multi-planar arm responses were observed bilaterally. The arm contralateral to the slipping foot demonstrated significantly greater excursion in the frontal plane than the ipsilateral arm (p < 0.001), whereas excursions in the sagittal plane did not differ between arms (p = 0.75). Further, the frontal plane excursion of the contralateral arm was greater than sagittal plane excursion (p < 0.001). The electromyographic onset of deltoid activity was equivalent in both arms (57-76 ms), despite the differences in kinematics. Multi-plane arm motion occurs in response to a slip perturbation. Specifically, frontal plane motion of the arm contralateral to the slipping foot exhibited the greatest amount of excursion.