Temporal dissociation between heart rate recovery and heart rate variability recovery after submaximal exercise in healthy older adults

BACKGROUND: Heart rate recovery (HRR) is commonly used to evaluate post-exercise recovery. However, it might not fully represent the recovery of heart rate variability-derived autonomic indices in older adults. This study examined whether heart rate and heart rate variability-derived indices of cardiac autonomic modulation show divergent recovery patterns following submaximal exercise in healthy older adults. METHODS: Fifty-eight community-dwelling adults aged 60-81 years completed a 5-minute submaximal step test following a 10-minute seated resting period. Heart rate (HR) and heart rate variability (HRV) parameters (RMSSD, pNN50, mean RR, SDNN, LF, HF, LF/HF ratio) were recorded during a 10-minute passive recovery period using a chest strap (Polar H10) monitor and analyzed with Kubios HRV software (version 4.0.3). Recovery dynamics were evaluated by comparing baseline values with the final 5-minute segment of the recovery phase. RESULTS: Heart rate and mean RR approached pre-exercise resting values during recovery, corresponding to 97.3% and 97.2% recovery, respectively. In contrast, RMSSD and pNN50 showed lower recovery ratios, corresponding to 79.8% and 51.1% of pre-exercise resting values, respectively. ΔHR showed a very strong association with Δ mean RR (r s = -0.932) but only moderate correlations with HRV-derived indices (ΔRMSSD: rs= -0.478; ΔHF: rs = -0.330). Recovery of HRV-derived indices was lower in the older-old group (75-81 years) and was associated with advancing age (ΔRMSSD: rs = -0.312; ΔHF: rs = -0.441). CONCLUSION: In healthy older adults, heart rate approached pre-exercise resting values during the post-exercise recovery period, whereas several HRV-derived indices remained incompletely restored. These findings suggest that heart rate and HRV-derived indices may follow different recovery trajectories after submaximal exercise. Because autonomic function was assessed using non-invasive measures, these findings should not be interpreted as direct evidence of a causal dissociation between heart rate recovery and parasympathetic reactivation.