Aerobic training improves vagal reactivation regardless of resting vagal control

Resting cardiac vagal modulation (RCVM) and postexercise vagal reactivation (PEVR) are markers of parasympathetic activity. We investigated whether adaptations in these markers to aerobic training are influenced by baseline autonomic control.

Forty healthy men (19.2 ± 0.8 yr) of similar cardiorespiratory fitness (VO₂peak = 50.4 ± 5.7 mL·kg⁻¹·min⁻¹) completed the study, being matched for autonomic activity and randomized into four groups: training low-RCVM (TL; n = 11, high-frequency power component [HF] = 48.1 ± 8.2 normalized units [n.u.]) and high-RCVM (TH; n = 11, HF = 63.1 ± 5.9 n.u.) and nonexercise control low-RCVM (CL; n = 9, HF = 47.1 ± 7.5 n.u) and high-RCVM (CH; n = 9, HF = 65.5 ± 8.3 n.u.). Aerobic training groups exercised 3 d·wk⁻¹ for 40 min at 75%-85% HR reserve for 12 wk. Before and after the training period, sequences of 5-min R-R intervals were recorded at rest and immediately after maximal treadmill test to estimate (a) RCVM (HF) and (b) PEVR (root mean square of successive R-R differences-rMSSD(3-5min) = mean value from 3 to 5 min of recovery).

Training improved VO₂peak in TL (11.7% ± 5.4%, P < 0.01) and TH (7.0% ± 2.9%, P < 0.01), with no difference between groups (P = 0.70), but not in CL (0.8% ± 3.9%) and CH (1.8% ± 6.2%, P = 0.90). Only TL increased RCVM (56.6 ± 13.3 n.u., P = 0.03), approaching TH level (58.9 ± 12.3 n.u.; P = 0.60); rMSSD(3-5min) increased in both training groups (P < 0.01) but not in controls (P = 0.99). Relative changes in RCVM (ΔHF%) and PEVR (ΔrMSSD(3-5min)%) were significantly correlated in TL (r = 0.61, P = 0.04).

PEVR after exercise increased in both exercise training groups, whereas RCVM increased only in the group with low vagal activity at baseline. Vagal reactivation may be improved by aerobic training, even when basal activity remains unaltered.