EXERCISE DOSE FOR CARDIOVASCULAR HEALTH OF OBESE YOUTHS

Abstract

Heart rate variability (HRV), analysis of beat-to-beat variation on a continuous ECG, provides a non-invasive method of assessing parasympathetic activity (PSA) and sympathetic neural activity (SNA) of the heart. The effect on HRV and CV health of lifestyle education (LSE) alone versus LSE+physical training (PT) at moderate and high intensities was investigated in obese youths. Subjects were 81 obese teenagers (14.9 ± 1.3 yr) assigned to: (1) biweekly LSE only; (2) LSE+moderate-intensity PT; or (3) LSE+high-intensity PT for 8 months, 5 days/week. The target energy expenditure (EE) for all subjects in both PT groups was 1047 kJ (250 kcal)/session. HRV parameters included two indices of PSA (root mean square of successive differences, RMSSD, and high frequency power, HFP) and an index of SNA (LFP/HFP ratio). CV fitness was measured using a treadmill test (VO2-170) and visceral adipose tissue (VAT) was measured with magnetic resonance imaging. Although the PT had favorable effects on VAT and VO2-170 (p's < 0.05), it did not lead to significant group differences in HRV parameters (p > 0.05). Within the PT group, those youths who maintained higher HR (r = 0.42, P < 0.01) and higher EE (r = 0.48, P < 0.01) during the PT tended to show increases in RMSSD from pre- to post-PT. Similarly, HFP tended to increase more in youths with higher EE (r = 0.36, P < 0.05) during PT. Those with higher attendance tended to have reductions in the change of LFP/HFP ratio (r = 0.32, P < 0.05). Thus, no experimental evidence was provided that those in the PT group improved significantly more than those in the LSE-alone group. However, within the groups that were assigned to PT, those who attended more regularly and exercised at a higher intensity showed more favorable changes in cardiac autonomic activity. Supported by NIH HL55564.