Autonomic Nervous System Modulation During a Moderate Exercise Session in Overweight and Normal Weight Individuals

Abstract

Autonomic nervous system (ANS) activity in overweight individuals has been characterized by low parasympathetic (PNS) and elevated sympathetic (SNS) activity. Continuously elevated SNS activity has been associated with an increased risk of cardiac complications. Thus, individuals at high risk for experiencing a cardiac event should be cautious of exaggerated elevations in SNS activity during and after physical exertion. PURPOSE: To assess ANS modulation via heart rate variability (HRV) in overweight and normal weight individuals prior to, during, and following moderate exercise. METHODS: Four overweight and obese (OW; 4 males; age: 27.5±3.1 years; BMI: 31.3±5.4 kg/m2) and four normal weight (NW; 2 males and 2 females; age: 27.5±3.4 years; BMI 23.2±1.4 kg/m2) adults participated in this study. During the initial visit, height, weight, and maximal oxygen consumption (VO2max) were evaluated. On a separate day, participants were asked to be seated at rest for 10 min and then cycled for 15-min at 75% of their VO2max. HRV indices [low and high frequency bands, their ratio, the square root of the mean of squared differences between successive RR intervals (RMSSD), and the percentage of successive normal-to-normal intervals greater than 50 ms (pNN50)] and respiratory rate were measured for 10-min at baseline, 10-min during exercise, and 10-min post-exercise. RESULTS: BMI was significantly different between groups (P<0.05). Heart rate was significantly higher during exercise in OW (148.1±10.6 bpm) compared to NW (130.1±6.8 bpm) (P<0.05). RMSSD was significantly different between groups during exercise (OW: 2.5±0.5 ms; NW: 5.0±1.9 ms) and at post-exercise (OW: 8.7±3.9 ms; NW: 21.5±7.8 ms). PNN50 was significantly lower in OW (0.2±0.3%) compared to NW (2.5±1.7%) at post-exercise. Respiratory rate was similar between groups at all time points. CONLUSION: These data suggest that ANS modulation in overweight and obese individuals during and immediately following exercise is characterized by low PNS and high SNS activity, compared to normal weight individuals exercising at the same relative intensity. Future research should further investigate the relationship between post-exercise ANS activity and the risk of cardiac complications, particularly among exercising overweight and obese individuals.