Novel Evidence of Cortical Control in Severe Slip Responses

Slips and falls are a major cause of injury and death in the United States. During a human slip response, an ensemble of muscular activations appear in an attempt to maintain balance and prevent a fall. The slip response has several key events that appear reflexive in nature. Though, the temporal nature of these responses may suggest cortical involvement as well. Indeed, some other forms of postural perturbations have provided evidence of cortical control in the recovery response. However, there is little information regarding cortical contribution to the slip response. PURPOSE: To examine corticospinal activity in lower extremity slip recovery corrective responses across slip severity. METHODS: One hundred participants were recruited for this study, and after exclusions the final analysis included 73 participants. Participant’s lower extremity gait kinematics, kinetics, and electromyography (EMG) on the quadriceps (Q), hamstrings (H), dorsiflexors (TA), and plantarflexors (MG) were collected during normal gait (NG) and an unexpected slip (US). The slip was classified based on slip severity, using heel slip distance, and velocity. Once classified, EMG spectral power was examined in the Piper frequency band between gait trials, and groups using a mixed model analysis of variance. RESULTS: Spectral power showed no differences in NG trials. However, spectral power in the Piper frequency band was increased in the Q and H, during the US trial for severe slips, but not minor slips. For the quadriceps, a significant gait by slip severity interaction was observed (F(1,70) = 9.934, p = 0.002, η2 = 0.124). Simple effects revealed a significant increase in activation between normal gait and unexpected slips for those who experienced hazardous slips (p \u3c 0.001), but no differences for non-hazardous slips (p = 0.364). For the hamstrings, a significant interaction was also observed (F(1,70) = 5.076, p = 0.027, η2 = 0.069). The simple effects revealed a significant increase in activity between gait trials, in the hazardous slips (p = 0.002), but not in the non-hazardous slips (p = 0.651). CONCLUSIONS: We show here novel contributions of the corticospinal pathway to the slip recovery response, particularly in musculature used in the recovery response