Mechanisms for Increases in (V) over dotO2max with Endurance Training in Older and Young Women

MURIAS, J. M., J. M. KOWALCHUK, and D. H. PATERSON. Mechanisms for Increases in (V) over dotO(2max) with Endurance Training in Older and Young Women. Med. Sci. Sports Exerc., Vol. 42, No. 10, pp. 1891-1898, 2010. Purpose: To examine the time course and mechanisms of cardiorespiratory fitness adaptation to training in older (O) and young (Y) women. Methods: A total of six O (69 +/- 7 yr) and eight Y (25 +/- 5 yr) women were examined before training and after 3, 6, 9, and 12 wk of training. Training was performed on a cycle ergometer three times per week for 45 min at similar to 70% of (V) over dotO(2max). Results: (V) over dotO(2max) (mL.kg(-1).min(-1)) increased within 3 wk, with further changes observed at weeks 6 and 9 in both O (17% +/- 14%) and Y and also posttraining (12 wk) in Y (22% T 6%, P < 0.05). Maximal cardiac output ((Q) over dot(max), open-circuit acetylene) and stroke volume increased only in Y after 9 wk of training (P +/- 0.05). Age x testing time interactions in maximal arterial-venous O-2 difference (a-vO(2diff)) after 6 wk of training revealed a greater dependence on a-vO(2diff) in O compared with Y (P < 0.05); similar to 65% of the change in (V) over dotO(2max) from pretraining to posttraining was explained by a widened maximal avO(2diff) in O compared with almost equal increases in (Q) over dot(max) and maximal a-vO(2diff) in Y. The early adaptations (first 3 wk) in O relied exclusively on a nonsignificant increase in (Q) over dot(max), whereas Y depended on a widened maximal a-vO(2diff). Later changes in (V) over dotO(2max) were explained exclusively by an improved maximal a-vO(2diff) in O and a larger (Q) over dot(max) in Y. Conclusions: O and Y women displayed a different time course of training adaptation in (V) over dotO(2max), with Y (after an initial improvement in maximal a-vO(2diff)) depending more on changes in (Q) over dot(max) and O mostly relying on a widened maximal a-vO(2diff).