Time course and mechanisms of adaptations in cardiorespiratory fitness with endurance training in older and young men

J Appl Physiol (1985). 2010 Mar;108(3):621-7. doi: 10.1152/japplphysiol.01152.2009. Epub 2010 Jan 7.


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 approximately 70% of maximal oxygen uptake (Vo(2 max)). Vo(2 max) increased within 3 wk with further increases observed posttraining in both O (+31%) and Y (+18%), (P < 0.05). Maximal cardiac output (Q(max), 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-vO(2 diff)) was higher at weeks 3 and 6 and posttraining compared with pretraining in O and Y (P < 0.05). In O, approximately 69% of the increase in Vo(2 max) from pre- to posttraining was explained by an increased Q(max) with the remaining approximately 31% explained by a widened a-vO(2 diff). This proportion of Q and a-vO(2 diff) contributions to the increase in Vo(2 max) was consistent throughout testing in O. In Y, 56% of the pre- to posttraining increase in Vo(2 max) was attributed to a greater Q(max) and 44% to a widened a-vO(2 diff). Early adaptations (first 3 wk) mainly relied on a widened maximal a-vO(2 diff) (approximately 66%) whereas further increases in Vo(2 max) were exclusively explained by a greater Q(max). In conclusion, with short-term training O and Y significantly increased their Vo(2 max); however, the proportion of Vo(2 max) increase explained by Q(max) and maximal a-vO(2 diff) throughout training showed a different pattern by age group.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological
  • Adolescent
  • Adult
  • Age Factors
  • Aged
  • Bicycling
  • Cardiac Output
  • Heart Rate
  • Humans
  • Male
  • Middle Aged
  • Muscle, Skeletal / blood supply
  • Muscle, Skeletal / metabolism*
  • Oxygen / blood*
  • Oxygen Consumption*
  • Physical Endurance*
  • Stroke Volume
  • Time Factors
  • Young Adult


  • Oxygen