Exercise Selection and Rest Interval Duration Differentially Affect Post-Exercise Cardiac Autonomic Responses Following Resistance Training

Objectives: This study investigated the effects of exercise selection and rest interval duration on post-exercise cardiac autonomic modulation following resistance exercise (RE). Methods: Eleven (4 females) resistance-trained individuals performed a single RE session consisting of either a multi-joint exercise (back squat) or a single-joint exercise (leg extension), using rest intervals of 1 or 2 min between sets. Heart rate variability (HRV) was assessed at baseline (pre-exercise) and 30 min following the RE session. RR intervals were recorded for 15 min with participants resting in the supine position on an examination bed in a quiet environment. For HRV analysis, a 5-min artifact-free segment of RR intervals was selected and processed using Kubios HRV software, version 4.3.0 (Kubios Oy, Kuopio, Finland). The HRV metrics analyzed included the root mean square of successive differences (RMSSD), low-frequency normalized (LF), the low-frequency/high-frequency (LF/HF) ratio, and the standard deviation of transverse dispersion (SD1). Results: A significant main effect of time was observed for RMSSD, LF, and the LF/HF ratio. The back squat exercise elicited a significant reduction (p < 0.05) in vagal-related indices (RMSSD and SD1) regardless of interval duration. Longer rest intervals were associated with increased (p < 0.05) sympathetic modulation, as reflected by higher LF and LF/HF values 30 min post-exercise. No significant time × group interactions were observed for most HRV variables. Conclusions: Exercise selection and rest interval duration differentially influence post-exercise cardiac autonomic responses following RE. Multi-joint exercises induce greater vagal withdrawal, whereas longer rest intervals favor sympathetic predominance during recovery. These findings highlight the importance of manipulating RE variables to manage autonomic stress and recovery.