A 30-year follow-up of the Dallas Bed rest and Training Study I. Effect ofage on the cardiovascular response to exercise

Background-Cardiovascular capacity declines with aging, as evidenced by dec lining maximal oxygen uptake (V) over dot(O2)max), with little known about the specific mechanisms of this decline. Our study objective was to assess the effect of a 30-year interval on body composition and cardiovascular res ponse to acute exercise in 5 healthy subjects originally evaluated in 1966. Methods and Results-Anthropometric parameters and the cardiovascular respon se to acute maximal exercise were assessed with noninvasive techniques. On average, body weight increased 25% (77 versus 100 kg) and percent body fat increased 100% (14% versus 28%), with little change in fat-free mass (66 ve rsus 72 kg). Oil average, (V) over dot(O2)max decreased 11% (3.30 versus 2. 90 L/min). Likewise, ((V) over dot(O2)max decreased when indexed to total b ody mass (43 versus 31 mL (.) kg(-1) (.) min(-1)) or fat-free mass (50 vers us 43 mL/kg fat-free mass per minute). Maximal heart rate declined 6% (193 versus 181 bpm) and maximal stroke volume increased 16% (104 versus 121 mL) , with no difference observed in maximal cardiac output (20.0 versus 21.4 L /min). Maximal AV oxygen difference declined 15% (16.2 versus 13.8 vol%) an d accounted for the entire decrease in cardiovascular capacity. Conclusions-Cardiovascular capacity declined over the 30-year study interva l in these 5 middle-aged men primarily because of an impaired efficiency of maximal peripheral oxygen extraction. Maximal cardiac Output was maintaine d with a decline in maximal heart rate compensated for by an increased maxi mal stroke volume. Most notably, 3 weeks of bedrest in these same men at 20 years of age (1966) had a more profound impact on physical work capacity t han did 3 decades of aging.