Running economy deteriorates following 60 min of exercise at 80% VO2max.

Fifteen young adult Singaporean male physical education students maximum oxygen consumption [(VO2max) = 56 (4.7) ml x kg(-1) min(-1)] performed three prolonged runs in a counterbalanced design. The running bouts varied in time (40 vs 60 min) and intensity (70% vs 80% VO2max). Each prolonged run was separated by 7 days. The running economy (RE) at 10.8 km x h(-1) during 10-min running bouts was measured before (RE1) and after (RE2) each prolonged run. A control study involved monitoring RE at 10.8 km x h(-1) before and after 60 min rest. There were no differences between RE1 and RE2 values during the control run. However, there were differences between RE1 and RE2 values when separated by a prolonged run. For example, the mean (SD) changes in oxygen consumption (ml x kg(-1) x min[-1]) values were 38.2 (2.5) versus 40.1 (2.6) (40 min at 80% VO2max), 38.9 (2.8) versus 41.5 [2.6] (60 min at 70% VO2max), and 39.0 (3.1) versus 42.7 (2.9) (60 min at 80% V02max; P < 0.01). The results of this investigation support the hypothesis that RE deteriorates during prolonged running, and that the magnitude of the deterioration in RE increases with both increasing exercise intensity and duration.