The purpose of this study was to examine the association of free-living, objectively-measured physical activity on treadmill-based heart rate recovery (HRR), a parameter known to associate with morbidity and mortality. Data was used from 2003 to 2004 NHANES. Physical activity was assessed via accelerometry, with HRR recovery assessed from a treadmill-based test. Heart rate recovery minute 1 (HRR1) and minute 2 (HRR2) were calculated. After adjustment, light and vigorous-intensity free-living physical activity, respectively, were associated with HRR1 (βadjusted = 0.69, 95% CI 0.22-1.14; βadjusted 1.94, 95% CI 0.01-3.9) and HRR2 (βadjusted = 0.99, 95% CI 0.35-1.62; βadjusted = 5.88, 95% CI 2.63-9.12). Moderate physical activity was not associated with HRR1 (βadjusted = 0.60, 95% CI -0.41 to 1.62), but was with HRR2 (βadjusted = 2.28, 95% CI 1.27-3.28). As free-living physical activity intensity increased, there was a greater association with HRR. This finding may provide mechanistic insight of previous research observations demonstrating intensity-specific effects of physical activity on various health outcomes.
Keywords: Accelerometry; Autonomic nervous system; Baroreflex sensitivity; Vagal tone.