Relations between insulin sensitivity, fitness and autonomic cardiac regulation in healthy, young men.

Objectives We hypothesized that insulin sensitivity and vagal cardiac control are independently related in young men after adjustment for fitness and other confounding variables. Design Male volunteers aged 21-24 years with high (borderline hypertensive; n = 20) and low-normal (normotensive; n = 21) screening blood pressure (BP) were studied cross-sectionally. Methods Mean R-R interval (RR) and heart rate variability (HRV) were computed from 30-min ECGs, and baroreflex sensitivity (BRS) and latency (phase shift) from 15-min beat-to-beat finger blood pressure (BP) and heart rate recordings. Insulin-adjusted glucose disposal rate (GDR/I) was measured with a 90-min hyperinsulinaemic glucose clamp and fitness by peak oxygen uptake (VO 2peak ) during a treadmill test Results HRV, baroreflex function, GDR/I, and VO 2peak did not differ between the groups. GDR/I correlated positively with time and frequency domain HRV, including highfrequency power (HF) (r= 0.40, P= 0.01) and root-mean squared successive differences (RMSSD) (r=0.43, P=0.005), but not BRS or phase shift GDR/I correlated with VO 2peak (r=0.70, P< 0.0001) and was explained (R 2 =0.56) by VO 2peak (β=0.57, P<0.0001) and RR (β=0.29, P= 0.03), independently of HRV and measures of obesity. Conversely, RR (β = 0.55, P = 0.0004) and HRV, including HF (β = 0.44, P = 0.006) and RMSSD (β = 0.46, P= 0.004) were explained by GDR/I, independently of VO 2peak . Conclusions Insulin sensitivity and autonomic cardiac control are related independently of physical fitness in young men.