Parasympathetic Modulation At Rest, During Exercise And Recovery From Maximal Exercise, In Boys And Men

Abstract

PURPOSE: Assess heart rate variability (HRV) to examine the parasympathetic nervous system (PNS) response from rest to light- (LIE) to moderate-intensity exercise (MIE) and recovery from maximal exercise in pre- (n = 10; maturity offset (MO) = -3.0 ± 1.2 yrs; age = 10.1 ± 1.9 yrs), mid- (n = 9; MO = -0.1 ± 0.6 yrs; age = 13.7 ± 1.0 yrs), and post-pubertal (n = 10; MO = 1.9 ± 0.6 yrs; age = 15.6 ± 1.2 yrs) boys and men (n = 10; age = 24.1 ± 2.0 yrs). METHODS: Subjects completed seated rest, LIE (50% HRmax) and MIE (65% HRmax). Intensity was then ramped to elicit maximal HR, followed by a 25-min seated recovery. HRV (root mean square of successive differences [RMSSD] and high-frequency power [HF]) was assessed during the last 3 min of rest, LIE and MIE and 3-min epochs ending at 10, 15, 20 and 25 min in recovery. RMSSD and HF were natural log transformed (ln) due to non-normal distribution. Significance was established if p ≤ 0.05. RESULTS: In each group, lnRMSSD and lnHF were similar at rest and decreased from rest to LIE to MIE. During LIE, lnRMSSD was greater in pre (3.4 ± 0.3 ms) than men (2.8 ± 0.5 ms) but similar to mid (3.1 ± 0.5 ms) and post (3.0 ± 0.5 ms). During MIE, lnRMSSD was similar between groups (pre = 2.1 ± 0.4 ms; mid = 1.9 ± 0.5 ms; post = 1.7 ± 0.5 ms; men = 1.8 ± 0.6 ms). Pre had greater lnHF than men during LIE (5.4 ± 0.7 ms2 vs 4.0 ± 0.9 ms2) and MIE (2.8 ± 1.0 ms2 vs 1.4 ± 1.0 ms2), but similar to mid (LIE = 4.8 ± 1.2 ms2; MIE = 2.3 ± 1.7 ms2) and post (LIE = 4.9 ± 0.9 ms2; MIE = 2.2 ± 0.8 ms2) at each intensity. In recovery, groups increased lnRMSSD from 10 (pre = 3.2 ± 0.8 ms; mid = 2.4 ± 0.6 ms; post = 1.8 ± 0.8 ms; men = 1.9 ± 0.5 ms) to 25 min (pre = 3.8 ± 0.6 ms; mid = 3.4 ± 0.6 ms; post = 2.8 ± 0.8 ms; men = 2.7 ± 0.8 ms). For lnHF, all groups increased from 10 (pre = 4.9 ± 1.8 ms2; mid = 3.4 ± 1.2 ms2; post = 2.2 ± 1.8 ms2) to 25 min (pre = 6.5 ± 1.3 ms2; mid = 5.6 ± 1.5 ms2; post = 4.1 ± 1.7 ms2), except men (2.5 ± 1.0 ms2 vs 3.9 ± 1.6 ms2; p = 0.09). At all points, lnRMSSD and lnHF were greater in pre compared to post and men. Also, mid and post had different lnRMSSD at 15 min (2.9 ± 0.7 ms vs 2.0 ± 0.7 ms) and lnHF at 20 min (5.5 ± 1.4 ms2 vs 3.7 ± 1.2 ms2). CONCLUSIONS: The primary findings were PNS withdrawal was reduced in pre-pubertal boys than men during LIE and MIE (HF only). Otherwise, MO did not affect PNS response from rest to MIE. Throughout recovery, PNS reactivation was greater in pre-pubertal boys compared to post-pubertal boys and men.