Physiological factors associated with the lower maximal oxygen consumption of master runners

We examined the hemodynamic factors associated with the lower maximal O ₂ consumption (V̇O(2max)) in older formerly elite distance runners. Heart rate and V̇O ₂ were measured during submaximal and maximal treadmill exercise in 11 master [66 ± 8 (SD) yr] and 11 young (32 ± 5 yr) male runners. Cardiac output was determined using acetylene rebreathing at 30, 50, 70, and 85% V̇O(2max). Maximal cardiac output was estimated using submaximal stroke volume and maximal heart rate. V̇O(2max) was 36% lower in master runners (45.0 ± 6.9 vs. 70.4 ± 8.0 ml·kg ^-1·min ^-1, P ≤ 0.05), because of both a lower maximal cardiac output (18.2 ± 3.5 vs. 25.4 ± 1.7 l·min ^-1) and arteriovenous O ₂ difference (16.6 ± 1.6 vs. 18.7 ± 1.4 ml O ₂·100 ml blood ^-1, P ≤ 0.05). Reduced maximal heart rate (154.4 ± 17.4 vs. 185 ± 5.8 beats·min ^-1) and stroke volume (117.1 ± 16.1 vs. 137.2 ± 8.7 ml·beat ^-1) contributed to the lower cardiac output in the older athletes (P ≤ 0.05). These data indicate that V̇O(2max) is lower in master runners because of a diminished capacity to deliver and extract O ₂ during exercise.