EFFECT OF A PHYSICAL ACTIVITY INTERVENTION ON HEART RATE VARIABILITY IN BLACK GIRLS

Abstract

PURPOSE To evaluate the impact of a 10-mo physical activity (PA) intervention on heart rate variability (HRV) and how the change in HRV was associated with changes in fitness and fatness. METHODS Black girls (n = 118), 8–12 y of age, were randomized to a PA or control group. HRV was measured with the subject resting quietly in a supine position while capturing 256 beats on a continuous ECG following 5–10 min of rest. HRV parameters included the root mean square of successive differences (RMSSD), low frequency power (LFP), high frequency power (HFP), and LFP/HFP ratio. Percent body fat (%BF) was measured using dual-energy x-ray absorptiometry. Cardiovascular fitness (CVF) was measured by a graded treadmill test. RESULTS 72 subjects completed the HRV, %BF and CVF measures before and after the intervention period (PA = 41, control = 31). The mean change in LFP/HFP ratio decreased in the PA group (mean ± SE: −0.13 ± 0.09) while it increased in the control group (0.16 ± 0.10) (p < 0.05 for the PA vs. control group comparison). The group differences in other HRV parameters were not significant (all p values > 0.05). The individual HRV changes over the 10-mo intervention period were not significantly associated with individual changes in CVF or %BF. CONCLUSION The only HRV measure that was significantly influenced by the PA intervention was the LFP/HFP ratio, suggesting an improvement in sympathetic – parasympathetic balance in the autonomic control of the heart. Supported by NIH (NHLBI 64972).