Acute autonomic modulation during Jacobson's progressive muscle relaxation in normal-weight vs. overweight male...

Heart rate variability (HRV) is a reliable non-invasive marker of autonomic nervous system (ANS) activity and has been increasingly used to assess physiological responses to stress and recovery interventions. Although relaxation techniques such as Jacobson’s Progressive Muscle Relaxation (PMR) are widely implemented, their acute effects on HRV across individuals with different body mass index (BMI) classifications (normal, overweight, obese) remain understudied. This study aimed to analyse HRV-based autonomic modulation during a Jacobson’s progressive muscle relaxation, and to assess differences between normal-weight and overweight recreational athletes. Sixty-three young male recreational athletes (23.8 ± 3.6 years) were assigned to normal-weight (BMI < 25, n = 38) or overweight (BMI ≥ 25, n = 25) group based on BMI. Participants underwent a standardized PMR protocol in a supine position with eyes closed. HRV, cortical arousal, perceived stress, and physical performance were assessed before, during, and after the intervention. During the relaxation phase with PMR, autonomic changes were observed reflecting parasympathetic dominance. Specifically, Heart Rate (HR) and Low Frequency (LF) power decreased significantly (partial η² = 0.28, 90% CI [0.16, 0.39]; partial η² = 0.31, 90% CI [0.19, 0.42]), while Root Mean Square of Successive Differences (RMSSD), pNN50, SD1/SD2 ratio, and High Frequency (HF) power increased (partial η² = 0.09 to 0.35, 90% CI [0.02, 0.14] to [0.22, 0.46]; all p < 0.001). Notably, the increases in RMSSD and pNN50 were specific to the overweight group (Group × Time interaction: partial η² = 0.07, 90% CI [0.01, 0.15] for RMSSD; partial η² = 0.09, 90% CI [0.02, 0.17] for pNN50). Perceived stress scores also declined after the session in both groups (partial η² = 0.12, 90% CI [0.04, 0.22]). We observed autonomic changes during the PMR protocol (vagal rebound), as reflected by HRV parameters in both normal-weight and overweight recreational athletes. These findings indicate that HRV responses occurred during the PMR protocol, suggesting that acute autonomic modulation can be detected in this context regardless of BMI status.