Autonomic Nervous System Function After Dynamic Exertion Among Athletes At Medical Clearance Following Concussion

Abstract

The autonomic nervous system (ANS) is commonly disrupted following sport-related concussion (SRC), and safe return to play/activity (RTP/A) is predicated on physiological recovery of ANS and other inter-related subsystems. Ultrashort (<5 min) heart rate variability (HRV) following exercise may be a proxy measure of ANS function but has predominately been measured following aerobic exertion without sport-specific movements. Dynamic exertion involves rapid change-of-direction tasks at varying intensities to perturb the vestibular and ocular subsystems in addition to the ANS. To date, researchers have yet to examine ultrashort HRV following dynamic exertion among athletes at medical clearance to RTP/A. PURPOSE: Compare age-estimated percentage of heart rate (HR %max) throughout a dynamic exertion assessment, in addition to post-exertion blood pressure and ultrashort HRV outcomes between athletes upon RTP/A from SRC with healthy athletes. METHODS: A sample of 23 (Female = 10, 43.5%) athletes at medical clearance to RTP/A (CONCUSS) and 23 sex-, age-, and sport-matched healthy athletes (CONTROL) completed a 5-min seated rest period prior to and following the dynamic exertion test. The dynamic exertion test is comprised of a12-min treadmill run and a series of functional movements and change-of-direction tasks. The root-mean-square of the successive differences (RMSSD) and standard deviation of successive heart beats (SDNN) were obtained from the final 3-min of pre- and post-EXiT rest periods. Between-group comparisons were conducted with a series of independent sample t-tests for HR %max and blood pressure, and 2X2 (GROUP X TIME) ANOVAs for RMSSD and SDNN. RESULTS: Main effects were observed for GROUP whereby CONCUSS had lower (less variable) RMSSD (p = .049, Ƞp2 = .209) and SDNN (p = .047, Ƞp2 = .212) than CONTROL, and for TIME as a reduction in RMSSD (p < .001, Ƞp2= .740) and SDNN (p < .001, Ƞp2= .760). HR %max and blood pressure were similar between groups (p > .05). CONCLUSION: ANS dysfunction may persist beyond clinical recovery in some athletes returning to sport after SRC. This is the first study to report differences in HRV between recently concussed and healthy athletes after dynamic exertion. Future work should consider the role of ANS function post-exertion to improve medical clearance decision making.