Influence of age and physical activity on central hemodynamics and lung function in active adults.

Five female and seven male physically active adults were studied twice within a 13-yr interval. The individual state of physical activity was mainly unchanged. Maximal oxygen uptake (VO2 max) was reduced in all subjects except one female, in whom it remained unchanged. During maximal exercise, cardiac output (Q) in males was unchanged. In females, Q was significantly increased due to increased stroke volume (SV). In both sexes, the reduced VO2 max was explained by a smaller arteriovenous O2 difference (mixed venous O2 content (C-VO2) significantly increased). For a given submaximal VO2, Q was increased in both sexes and heart rate was unchanged. Thus, SV was increased and arteriovenous O2 difference was reduced due to increased C-VO2. Another four males were studied several times in various states of physical fitness during an 11-yr period. The reduced VO2 max from peak value was due to a reduced Qmax (SV smaller), whereas the arteriovenous O2 difference and C-VO2 were unchanged. Our results indicate that the observed changes in circulatory response to submaximal and maximal exercise in physically active adults may to a large extent be due to an effect of "detraining."