Cardiovagal modulation and efficacy of aerobic exercise training in obese individuals

Type 2 diabetes (T2D) is associated with poor exercise tolerance and peak aerobic capacity (VO_2peak) even when compared to obese nondiabetic peers. Exercise training studies have demonstrated improvements in VO _2peak among patients with T2D, yet there is a large amount of variability in this response. Recent evidence suggests that cardiac autonomic modulation may be an important factor when considering improvements in aerobic capacity. PURPOSE: This study aimed to determine the effects of a 16-wk aerobic exercise program on VO_2peak in obese individuals, with and without T2D, who were classified as having either high or low cardiovagal modulation (HCVM or LCVM) at baseline. METHODS: Obese individuals (38 women and 19 men; body mass index = 36.1 kg·m^-2) were studied in the fasted state. ECG recordings were obtained while seated for 3 min, before and after 4 months of exercise training (4 d·wk^-1, 65% VO _2peak). The ECG recording was analyzed for HR variability in the spectral domain. Groups were split on a marker of CVM (normalized high frequency (HFnu)) at the 50th percentile, as either HCVM or LCVM. RESULTS: VO _2peak only increased with exercise training among those classified as having HCVM, regardless of diabetes status (T2D: HCVM = 20.3-22.5 mL·kg^-1·min^-1, LCVM = 24.3-25.0 mL·kg^-1·min;^-1 obese nondiabetics: HCVM = 24.5-26.3 mL·kg^-1·min^-1, LCVM = 23.1-23.7 mL·kg^-1·min^-1) (P < 0.05). No change in VO_2peak was observed for the LCVM group. Changes in weight do not explain the change in VO_2peak among the HCVM group. Glucose tolerance only improved among the LCVM group with T2D. CONCLUSIONS: Obese individuals, with or without T2D, when classified as having relatively HCVM before exercise training, have a greater propensity to improve VO_2peak after a 16-wk aerobic training program.