Vagal modulation of heart rate during exercise: effects of age and physical fitness

TLDR

The study aimed to evaluate how age and physical fitness influence vagal modulation of heart rate during exercise by analyzing instantaneous R‑R interval variability from Poincaré plots in healthy men. SD1 normalized for the average R‑R interval (SD1 n) was compared at rest and during exercise across age groups (24–34, 35–46, 47–64) matched for VO₂ peak and across fitness levels (poor, average, good) matched for age. Results showed that young men had higher resting SD1 n than middle‑aged or older men, but age differences narrowed during exercise, while fitness level did not affect resting SD1 n yet produced significant differences during low‑to‑moderate exercise, indicating that poor fitness impairs vagal function during exercise whereas aging mainly reduces vagal function at rest.

Abstract

This study was designed to assess the effects of age and physical fitness on vagal modulation of heart rate (HR) during exercise by analyzing the instantaneous R-R interval variability from Poincaré plots (SD1) at rest and at different phases of a bicycle exercise test in a population of healthy males. SD1 normalized for the average R-R interval (SD1 n ), a measure of vagal activity, was compared at rest and during exercise among subjects of ages 24–34 (young, n = 25), 35–46 (middle-aged, n = 30), and 47–64 yr (old, n = 25) matched for peak O 2 consumption (V˙o 2 peak ) and among subjects withV˙o 2 peak of 28–37 (poor, n = 25), 38–45 (average, n = 36), and 46–60 ml ⋅ kg −1 ⋅ min −1 (good, n = 25) matched for age. SD1 n was higher at rest in the young subjects than in the middle-aged or old subjects (39 ± 14, 27 ± 16, and 21 ± 8, respectively; P < 0.001), but the age-related differences in SD1 n were smaller during exercise [e.g., 11 ± 5, 9 ± 5, and 8 ± 4 at the level of 100 W; P = not significant (NS)]. The age-matched subjects with good, average, and poor V˙o 2 peak showed no difference in SD1 n at rest (32 ± 17, 28 ± 13, and 26 ± 11, respectively; P = NS), but SD1 n differed significantly among the groups from a low to a moderate exercise intensity level (e.g., 13 ± 6, 10 ± 5, and 6 ± 3 for good, average, and poor fitness groups, respectively; P < 0.001, 100 W). These data show that poor physical fitness is associated with an impairment of cardiac vagal function during exercise, whereas aging itself results in more evident impairment of vagal function at rest.