Blood volume expansion and cardiorespiratory function: Effects of training modality

To evaluate the effects of different modalities of aerobic (i.e., interval (INT) and continuous (CONT)) training on cardiorespiratory function and the importance of training-induced blood volume (BV) expansion on aerobic power and LV function. We hypothesized that if modality-mediated differences in cardiorespiratory function exist after INT and CONT, they would be related directly to differences in training-induced hypervolemia. We examined the effects of 12 wk of CONT and INT on BV, volume-regulatory hormones (angiotensin II, aldosterone, atrial natriuretic peptide), and cardiorespiratory function in 20 untrained males (mean age 30 +/- 4 (SD)). Participants were stratified (mass and VO2max) and randomly assigned to control, CONT, or INT. There were no significant changes in cardiorespiratory function or BV in the control group. Twelve weeks of continuous and interval training, respectively, resulted in significant changes in VO2max (23 +/- 18 vs 21 +/- 10%), peak stroke volume (20 +/- 18 vs 11 +/- 18%), and BV (12 +/- 9 vs 10 +/- 6%). Changes in VO2max were directly related to changes in BV (r = 0.47). Angiotensin II significantly increased after 1 wk of CONT and INT and thereafter returned to baseline values. There was no significant difference between the CONT and INT groups with regard to changes in vascular volumes, volume-regulatory hormones, and/or cardiorespiratory function. These data indicate that: 1) 12 wk of CONT and INT result in similar improvements in VO2max, and LV function and 2) training-induced hypervolemia accounts for approximately 47% of the changes in VO2max after CONT and INT.