Time course and mechanisms of adaptations in cardiorespiratory fitness with endurance training in older and young men.
Level 3 - non-randomized controlled study
Prospective non-randomized comparative cohort study
PubMed 20056848 · doi:10.1152/japplphysiol.01152.2009
What was done
Eight older men (mean age 68 ± 7 years) and eight young men (mean age 23 ± 5 years) completed a 12-week endurance cycling protocol (3 sessions/week, 45 minutes at ~70% VO2 max). Cardiorespiratory fitness metrics—VO2 max, maximal cardiac output (Qmax via open-circuit acetylene), stroke volume, and maximal arterial-venous oxygen difference (a-vO2 diff)—were measured pre-training and at 3, 6, 9, and 12 weeks.
What was found
VO2 max increased significantly within 3 weeks, reaching post-training increases of +31% in older men and +18% in young men (P < 0.05). Qmax and stroke volume increased after 3 weeks with further increases after 9 weeks in both groups (P < 0.05). Maximal a-vO2 diff increased at weeks 3, 6, and post-training in both groups (P < 0.05). In older men, ~69% of the VO2 max increase was explained by increased Qmax and ~31% by widened a-vO2 diff, a proportion that remained consistent throughout training. In young men, 56% of the overall increase was attributed to Qmax and 44% to a-vO2 diff; early gains (first 3 weeks) were primarily driven by widened a-vO2 diff (~66%), while subsequent gains were explained exclusively by increased Qmax.
Why it matters
The study shows that older adults retain robust cardiorespiratory plasticity, achieving substantial VO2 max improvements driven primarily by central cardiovascular adaptations from the start of training.
Limits
The sample size was very small (n=8 per group, total n=16). The study included only men and lacked a non-exercising control group.
Cited by
- supports An increase in stroke volume is the primary physiological adaptation responsible for improvements in VO2 max.