Abstract
To test the hypothesis that autonomic modulation of heart rate is related to fitness and/or physical activity we measured indices of short term heart rate variability (HRV) during controlled frequency breathing (0.2 Hz) in the seated position and compared them with VO2MAX (incremental GXT), and calories/week from a standardized 7-day physical activity recall (PAR) interview. The subjects were sedentary individuals (137 M and 257 F, mean age 52.3, range 35-75) enrolled in the Activity Counseling Trial (ACT) study. HRV was measured in the time domain from the standard deviation (SDNN), variance(SDNN)2 and coefficient of variation (SD/mean = CV) of the R-R intervals and in the frequency domain by power spectral analysis of two, 256 beat epochs (mod. Welch method). Absolute (PSD) and normalized (norm) power were measured at low (LF, 0.04-0.15 Hz), high (HF, 0.15-0.5 Hz) and total power (TP, 0.01-0.5 Hz) and LF/HF ratio. Partial correlation coefficients (r) for VO2MAX or PAR vs. HRV were determined after removing effects of gender. Results: There was no significant correlation between HRV and PAR. For VO2max vs HRV (*P<0.05) VO2MAX = 23±6.5 ml/kg/min Table Although some of the r values are statistically significant no correlation appeared physiologically significant and < 5% of the variance in HRV could be explained by a variation in VO2MAX in this preliminary cross-sectional analyses of a sedentary population. We speculate that increases in fitness and activity will be associated with increases in HRV. This hypothesis will be tested in the ACT intervention study
Published Version
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