REGULATION OF BLOOD-VOLUME DURING TRAINING IN POSTMENOPAUSAL WOMEN

In younger people the increase in aerobic capacity following training is related, in part, to blood volume (BV) expansion and the consequent improvements in maximal cardiac output. This training-induced hypervo lemia is associated with a decrease in cardiopulmonary baroreflex (CPB R) control of peripheral vascular tone. Purpose: To test the hypothesi s that improvement in peak oxygen consumption ((V)over dot O-2peak) du ring training in older women is associated with specific central adapt ations, such as BV expansion and a reduction in CPBR control of vascul ar tone. Methods: Seventeen healthy older women were randomized into t raining (N = 9, 71 +/- 2 yr) and control (N = 8, 73 +/- 3 yr) groups. The training group exercised three to four times per wk for 30 min at 60% peak heart rate for 12 wk and then 40-50 min at 75% peak heart rat e for 12 wk. The control group participated in yoga exercises over the same time period. We measured resting BV (Evans blue dye), (V)over do t O-2peak, and the forearm vascular resistance response to unloading l ow pressure mechanoreceptors during low levels of lower body negative pressure (through -20 mm Hg) before and after aerobic training. The sl ope of the increase in forearm vascular resistance (response) per unit decrease in central venous pressure (stimulus) was used to assess CPB R responsiveness, Results: Aerobic training increased (V)over dot O-2p eak 14.2% from 24.2 mL.kg(-1).min(-1) to 27.7 mL.kg(-1).min(-1) (P < 0 .05), a smaller improvement than typically seen in younger subjects. B lood volume (59.9 +/- 1.9 and 60.9 +/- 1.9 mL.kg(-1)) and CPBR functio n (-3.98 +/- 0.92 and -3.46 +/- 0.94 units.mm(-1) Hg) were similar bef ore and after training. Conclusions: These data indicate that the inab ility to induce adaptations in CPBR function may limit BV expansion du ring training in older women. In addition, the absence of these specif ic adaptations may contribute to the relatively poor improvements in ( V)over dot O-2peak in older women during short (10-12 wk) periods of t raining.