The purpose of this study was to investigate the effect of prolonged exercise at 65 and 80% of VO2max on running economy. Fourteen male long distance runners performed two 90-min runs on an outdoor 400 m track at velocities of 65 and 80% of VO2max. Prior to and following each 90-min run, running economy was measured as the steady-state VO2 during treadmill runs at speeds of 188 and 228 m/min. During the 90-min run at 65% of VO2max, the mean weight loss was 1.3 kg. HR increased from 143 bpm between minutes 5-10 to 150 bpm between minutes 85-90. During the 90-min run at 80% of VO2max, the mean weight loss was 1.4 kg. The HR was 161 bpm between minutes 5-10 and increased to 165 bpm between minutes 85-90. When the post running economy test was conducted following each 90-min run, there was a significant increase in VO2 expressed in both l/min and ml/kg min. The increase in VO2 following the 90-min run at 80% of VO2max. These results suggest that 90-min runs at 65 and 80% of VO2max alter running economy with a significant increase in oxygen cost.
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