Heart rate variability responses to a combined exercise training program: correlation with adiposity and cardiorespiratory fitness changes in obese young men

Abstract

Although the influence of adiposity indices and cardiorespiratory fitness (CRF) on heart rate variability (HRV) has been demonstrated extensively, the causal link between the changes in adiposity as well as in CRF and the alterations in cardiac autonomic function is unclear. Thus, this study aimed to assess the correlation between the changes in adiposity and CRF and the alterations in HRV after 12-week exercise training. Twenty obese sedentary men aged 20.5±1.2 years were randomly assigned into 2 groups (n=10 each): the control (CG) and the exercise group (EG). The EG trained 60 min of combined aerobic, anaerobic and strengthening exercise, 4 sessions/wk for 12 weeks, whilst the CG remained relatively inactive. Measurements of resting HRV, body composition, and peak oxygen consumption (VO_2peak) were obtained at baseline and after the 12-week training program. Compared with CG, the exercise training significantly reduced adiposity indices and improved vagal-related HRV variables and VO_2peak. Significant correlations were observed between changes in HRV variables and adiposity indices and VO_2peak changes. Stepwise regression analysis revealed that changes in a Poincaré plot index (SD1/SD2 ratio) predicted 32.4% of the variance in the relative VO_2peak changes. These findings suggest that obese sedentary young men achieved significant improvements in vagal activity, adiposity indices and aerobic fitness after the exercise training. The higher reduction in fat mass, especially central obesity, the greater alteration of vagal modulation. Moreover, the alteration in resting HRV is a possible predictor for adaptations to exercise training in obese sedentary young men.

Keywords: Central obesity; Exercise test; Exercise training; Heart rate.

Fig. 1

Correlation between (A) the change in waist circumference and the change in pNN50 (r=0.495, P<0.05), (B) the change in waist-to-hip ratio and the change in mean RR intervals (r=−0.045, P<0.05), (C) the change in fat mass and the change in mean RR intervals (r=−0.502, P<0.05), (D) the change in relative VO_2peak and the change in pNN50 (r=0.471, P<0.05), (E) the change in relative VO_2peak and the change in the SD1/SD2 Poincaré plot index (r=0.57, P<0.01), (F) the change in relative VO_2peak and the change in the LF/HF ratio (r=−0.444, P<0.05). ●, EG group; ○, CG group; pNN50, percentage of successive RR intervals that differ by more than 50 msec; SD1, Poincaré plot standard deviation perpendicular the line of identity; SD2, Poincaré plot standard deviation along the line of identity; LF, low-frequency; HF, high-frequency; VO_2peak, peak oxygen consumption.