Cardiac autonomic function reveals adaptation to military training

The last 4 weeks of basic military training are very stressful. We tested the hypothesis that changes in cardiac autonomic function during this period are associated with changes in maximal oxygen uptake and/or serum hormonal concentrations in male conscripts (n = 22). Cardiac vagal autonomic function was assessed by measuring the high- frequency (0.15-0.4 Hz) spectral power of R-R intervals. Maximal oxygen uptake ((V) over dotO(2max)) and basal serum testosterone concentration were measured at the beginning and end of the period. Individual changes in vagally mediated high- frequency power (range -15% to +25%) correlated (r=0.73, P=0.001) with changes in (V) over dotO(2max) (range -9% to +6%) and changes in testosterone concentration (range -52% to +43%; r=0.43, P=0.047). The mean values of (V) over dotO(2max) and testosterone concentration did not change during the study period. Measurements of autonomic function could be a useful tool for indicating adaptation to the highly stressful conditions associated with basic military training.