A 30-year follow-up of the Dallas Bedrest and Training Study: I. Effect of age on the cardiovascular response to exercise.
Level 4 - case-series / case-control
Small single-cohort longitudinal follow-up study (n = 5) without a concurrent control group.
What was done
Five healthy men originally evaluated in 1966 in the Dallas Bedrest and Training Study were re-evaluated 30 years later. Anthropometric parameters and cardiovascular responses to acute maximal exercise were measured using noninvasive techniques to assess changes in body composition, maximal oxygen uptake (VO2max), central hemodynamics, and peripheral oxygen extraction.
What was found
Over 30 years, average body weight increased 25% (77 to 100 kg) and percent body fat increased 100% (14% to 28%), while fat-free mass changed from 66 to 72 kg. Mean VO2max declined 11% (3.30 to 2.90 L/min), dropping from 43 to 31 mL/kg/min indexed to body weight and from 50 to 43 mL/kg fat-free mass/min. Maximal heart rate fell 6% (193 to 181 bpm) and maximal stroke volume increased 16% (104 to 121 mL), resulting in unchanged maximal cardiac output (20.0 vs 21.4 L/min). Maximal arteriovenous oxygen difference declined 15% (16.2 to 13.8 vol%), accounting for the entire reduction in VO2max.
Why it matters
This study shows that over three decades of aging, the reduction in aerobic capacity was driven by impaired peripheral oxygen extraction rather than central circulatory limitations, which were preserved by compensatory stroke volume increases.
Limits
The sample size is extremely small (n = 5), limited strictly to healthy men, preventing generalization to women or broader populations. The abstract reports noninvasive assessments without a separate control cohort.
Cited by
- supports In the 30-year follow-up to the Dallas Bed Rest Study, participants' decline in cardiorespiratory fitness after 30 years of aging was no worse than their decline after 3 weeks of strict bed rest.