Mike G. Yandl, Brandon V. Reynolds, and William H. Cooke
YANDL, MICHAEL G., BRANDON V. REYNOLDS, WILLIAM H. COOKE, . Changes in maximal oxygen uptake (VO2max), cardiac autonomic function, baroreflex function, and orthostatic tolerance were assessed before and after 4 wk of moderate aerobic training (30 min on cycle ergometer, 3 days/wk, HR >= 70% of HRmax) in healthy, sedentary, young men (22.4 +/- 1.1 years, n = 9). Four weeks of exercise training increased VO2max (3.36 +/- 0.29 to 3.62 +/- 0.36 l/min, P < 0.05) and RRISD (89.06 +/- 36.91 to 105.61 +/- 48.46 ms, P < 0.05). Vagal and sympathetic baroreflex gain were determined from the RRI vs. SAP linear regression during phase IV of the Valsalva maneuver, and peroneal muscle sympathetic nerve activity vs. DAP relationship during phase II, respectively. Vagal baroreflex gain increased (14.38 +/- 4.14 to 27.72 +/- 16.33 ms/mmHg, P < 0.05) after training, however no significant change in sympathetic baroreflex gain was observed (10.75 +/- 7.14 to 10.38 +/- 7.54 ms, P > 0.05). No significant change was found in supine, resting MSNA (39.31 +/- 24.72 to 58.17 +/- 20.67 mV, P > 0.05, n =5) between pre- and post-training conditions. Furthermore, head-up tilt did not affect RRISD (49.56 +/- 16.38 to 54.56 +/- 15.95 ms, P > 0.05) or BRS (9.37 +/- 3.81 to 9.98 +/- 3.75 ms/mmHg, P > 0.05). Our results show that in healthy, sedentary, young males, short-term, moderate-intensity aerobic training: 1) increases maximal aerobic capacity; 2) increases cardiac vagal tone and vagal baroreflex gain at rest (shifting cardiac autonomic balance toward parasympathetic dominance); but 3) does not alter resting sympathetic nerve traffic; and 5)does not affect orthostatic tolerance. We conclude that significant improvements in autonomic cardiovascular control are obtainable after brief periods of exercise training, and that these improvements are prognostically healthy.
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