Vagal and cardiac reactivity to psychological stressors in trained and untrained men

Purpose: The aim of this study was to determine whether higher aerobic fitn ess is associated with enhanced vagal influences on the myocardium, resulti ng in moderation of chronotropic cardiac activity during psychological stre ss and recovery. Method: Heart period (HP) and respiratory sinus arrhythmia (RSA) were obtained from 10 aerobically trained (AT) and 10 untrained (UT) college-aged men at rest and during three contiguous psychological challen ges and 3 min of recovery. Ratings of perceived stress were obtained at the end of the rest period, at the midpoint of each stressor, and at 30 s into recovery. Time series methods were used to quantify RSA from the beat-to-b eat HP series. Responsivity was assessed both in terms of absolute levels o f activity and phasic changes in activity (task or recovery minus baseline) . Results: Both groups reported similar levels of subjective stress through out the experiment. The AT exhibited longer HP at rest and during psycholog ical stress and recovery than did the UT. However, the groups did not diffe r on RSA at rest or during. psychological stress and recovery, nor did they differ on phasic changes in RSA or HP during stress or recovery. Additiona lly, aerobic capacity was not correlated with absolute levels or phasic cha nges in RSA during psychological challenge for either group and, except in Min 2 for the UT, similar results were obtained for recovery. Conclusions: The results supported the hypothesis that, among young men, higher aerobic fitness is associated with longer HP at rest and during psychological stres s and recovery. However, the lower cardiac chronotropic activation observed among the AT relative to the UT was not paralleled by a group difference i n the amplitude of RSA. These results suggest that the group difference in HP was not mediated directly by the vagal mechanisms manifested in the ampl itude of RSA.