Short-term effects of weight-loading on heart rate variability in obese adults.

Weight-loading reduces body fat, but its effects on cardiac autonomic modulation remain unclear. We examined heart rate variability (HRV) during free-living weight-loading in adults with class I obesity. Fifty-one participants (27 females) were randomized to wear a heavy (11% of body weight) or a light vest (1%) for 8 h/day for 15 days. Twenty-four-hour ECG recordings were obtained before and on day 15. Heart rate (HR), relative HR reserve (%HRR), and time- and frequency-domain HRV indices were analyzed across four predefined periods: morning (rest), afternoon (vest-usage), evening, and night. During the afternoon period, the high versus low load increased HR (p = 0.0496) and %HRR (p = 0.03), while reducing SDNN (standard deviation of normal-to-normal intervals; p = 0.01) and RMSSD (root mean square of successive differences; p = 0.002). In females, but not in males, high load was associated with lower high-frequency power (PHF), higher low-frequency power (PLF), and an increased PLF/PHF ratio during the afternoon, consistent with reduced parasympathetic modulation. No differences between groups were observed during resting periods. These findings indicate that weight-loading increases cardiovascular workload and transiently alters autonomic modulation during active vest use, with more consistent responses in females and no sustained resting adaptations.