Physical fitness as a determinant of vagal modulation
Goldsmith, R.L.; Bigger, J.T.; Bloomfield, D.M.; Steinman, R.C.
Medicine and Science in Sports and Exercise 29(6): 812-817
1997
ISSN/ISBN: 0195-9131 PMID: 9219210 Document Number: 1124
The association between increasing age and decreasing vagal modulation is well known. However, the importance of fitness as a determinant of the decline in vagal modulation with age is not established. To test the hypothesis that decreasing vagal modulation is largely a function of declining fitness, rather than increasing age, we studied a sample of healthy volunteers with a wide range of fitness levels, but a narrow age range. We assessed fitness by measuring the maximal oxygen uptake ( ovrhdot VO-2max) achieved during incremental bicycle exercise. Vagal modulation was assessed by calculating high frequency power (0.15-0.40 Hz) of the RR variability power spectrum from 24-h ECG recordings. We studied 37 healthy volunteers who were 22-44 yr old. In our sample, ovrhdot VO-2max ranged from 25 to 70 mL cntdot min-1 cntdot kg-1 (mean of 45 +- 13). Age was not significantly related to high frequency power, but ovrhdot VO-2max was highly correlated with high frequency power (r = 0.74, P = 0.0001), indicating that physical fitness is strongly associated with vagal modulation. Thus, the decline in vagal modulation often attributed to increasing age may, instead, be the result of a decline in fitness.
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