Juan M. Murias, John M. Kowalchuk, Donals H. Paterson
Journal of Applied Physiology March 1, 2010vol. 108 no. 3 621-627

The time-course and mechanisms of adaptation of cardiorespiratory fitness were examined in 8 older (O) (68 ± 7 yr old) and 8 young (Y) (23 ± 5 yr old) men pretraining and at 3, 6, 9, and 12 wk of training. Training was performed on a cycle ergometer three times per week for 45 min at ∼70% of maximal oxygen uptake (V̇O2 max). V̇O2 max increased within 3 wk with further increases observed posttraining in both O (+31%) and Y (+18%), (P < 0.05). Maximal cardiac output (Q̇max, open-circuit acetylene) and stroke volume were higher in O and Y after 3 wk with further increases after 9 wk of training (P < 0.05). Maximal arterial-venous oxygen difference (a-vO2diff) was higher at weeks 3 and 6 and posttraining compared with pretraining in O and Y (P < 0.05). In O, ∼69% of the increase in V̇O2 max from pre- to posttraining was explained by an increased Q̇max with the remaining ∼31% explained by a widened a-vO2diff. This proportion of Q̇ and a-vO2diff contributions to the increase in V̇O2 max was consistent throughout testing in O. In Y, 56% of the pre- to posttraining increase in V̇O2 maxwas attributed to a greater Q̇max and 44% to a widened a-vO2diff. Early adaptations (first 3 wk) mainly relied on a widened maximal a-vO2diff (∼66%) whereas further increases in V̇O2 max were exclusively explained by a greater Q̇max. In conclusion, with short-term training O and Y significantly increased their V̇O2 max; however, the proportion of V̇O2 max increase explained by Q̇maxand maximal a-vO2diff throughout training showed a different pattern by age group.

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