The Effect of Anticipation on Calf Muscle Response to Standing Perturbations (2024)
Undergraduate: Lea Klissouras
Faculty Advisor: Jason Franz
Department: Biomedical Engineering
Falls pose a tremendous risk to older adults; understanding the mechanisms of muscle response to balance challenges is an imperative contribution to the development of training paradigms, assistive technologies, and clinical interventions that mitigate fall risk for vulnerable individuals. There is evidence that anticipation of a balance challenge is likely to augment force responsiveness of distal leg muscles based on voluntary proactive adjustments. However, there is a gap in studies analyzing ultrasound data that would provide vital context for the robustness of these responses. This study seeks to use metrics extracted from in vivo ultrasound data (i.e., fascicle length and velocity) to investigate the influence of anticipation on the proactive and reactive responses of the medial gastrocnemius to rapid surface translations. We hypothesized that, compared to unanticipated perturbations, anticipation would (1) augment the proactive response by increasing both length change and the magnitude of velocities, and (2) enhance the potential for force responsiveness during the reactive phase, as evidenced by decreased length changes and velocity magnitudes. 14 young adults were harnessed to an instrumented treadmill which rapidly decelerated and accelerated to simulate posterior and anterior standing slips. Three trials were performed for each perturbation condition: anticipated posterior, anticipated anterior, unanticipated posterior, and unanticipated anterior. In anticipated trials, a verbal countdown indicating slip direction was provided. Ultimately, anticipation resulted in statistically significantly slower lengthening velocities in the anterior direction (i.e. the direction that would precipitate backwards falls, which are more dangerous and result in more injury). These results indicate that force generation would be augmented for anterior perturbations. Accordingly, anticipation appears to be protective against perturbations that would elicit a backwards fall. Understanding the muscle fascicle response to anticipated perturbations in young adults will provide a comparative foundation for the response of populations more vulnerable to falls.