Axial muscle activation provides stabilization against perturbations while running.

Incidence of traumatic brain injury is an important hazard in sports and recreation. Unexpected (blind-sided) impacts with other players, obstacles, and the ground can be particularly dangerous. We believe this is partially due to the lack of muscular activation which would have otherwise provided protective bracing. In this study participants were asked to run on the treadmill while undergoing perturbations applied at the waist which pulled participants in the fore-aft and lateral directions. To determine the effect of unexpected impacts, participants were given a directional audio-visual warning 0.5 s prior to the perturbation in half of the trials and were unwarned in the other half of the trials. Perturbations were given during the start of the stance phase and during the start of the flight phase to examine two distinct points within the locomotor cycle. Muscle activity was monitored in axial muscles before, during, and after the perturbations were given. We hypothesized that the presence of a warning would allow for voluntary axial muscle activity prior to and during perturbations that would provide bracing of the body, and decreased displacement and acceleration of the head compared to unwarned perturbations. Our results indicate that when a warning is given prior to perturbation, the body was displaced significantly less, and the linear acceleration of the head was also significantly lessened in response to some perturbations. The perturbations given in this study caused significant increases in axial muscle activity compared to activity present during control running. We found evidence that cervical and abdominal muscles increased activity in response to the warning and that typically the warned trials displayed a lower reflexive muscle activity response. Additionally, we found a stronger effect of the warnings on muscle activity within the perturbations given during flight phase than those given at stance phase. Results from this study support the hypothesis that knowledge regarding an impending perturbation is used by the neuromuscular system to activate relevant core musculature and provide bracing to the athlete.