Heart rate variability and baroreceptor responsiveness to evaluate autonomic cardiovascular adaptations to exercise

Exercise physiologists routinely evaluate adaptations to exercise such as aerobic capacity, muscular strength and flexibility, and body composition, but often overlook the effects of exercise training on autonomic regulation of cardiovascular function. A preponderance of cross-sectional studies report significant resting sinus bradycardia and high heart rate variability in active subjects, and suggest that exercise training induces adaptations in autonomic cardiovascular control. Alternatively, data from cross-sectional studies leave open the possibility that individuals with a genetic predisposition for lower heart rates or greater heart rate variability are also endowed with greater aerobic capacity. Conflicting results from a limited number of exercise training studies fail to conclusively demonstrate a direct effect of exercise training on the autonomic nervous system. In this report I suggest that simple measures of heart rate variability during controlled frequency breathing, and arterial baroreceptor responsiveness to Valsalva's maneuver provide unique insights into autonomic regulation of cardiovascular function. I propose that systemic-wide integration of exercise training effects might be better characterized if exercise physiologists would perform tests of autonomic function in conjunction with standard exercise tests during routine laboratory evaluations.