Effect of exercise intensity on post-exercise oxygen consumption and heart rate recovery

There is some evidence that measures of acute post-exercise recovery are sensitive to the homeostatic stress of the preceding exercise and these measurements warrant further investigation as possible markers of training load. The current study investigated which of four different measures of metabolic and autonomic recovery was most sensitive to changes in exercise intensity. Thirty-eight moderately trained runners completed 20-min bouts of treadmill exercise at 60, 70 and 80 % of maximal oxygen uptake (VO2max) and four different recovery measurements were determined: the magnitude of excess post-exercise oxygen consumption (EPOCMAG), the time constant of the oxygen consumption recovery curve (EPOC tau), heart rate recovery within 1 min (HRR60s) and the time constant of the heart rate recovery curve (HRR tau) . Despite significant differences in exercise parameters at each exercise intensity, only EPOCMAG showed significantly slower recovery with each increase in exercise intensity at the group level and in the majority of individuals. EPOC tau was significantly slower at 70 and 80 % of VO2max vs. 60 % VO2max and HRR tau was only significantly slower when comparing the 80 vs. 60 % VO2max exercise bouts. In contrast, HRR60s reflected faster recovery at 70 and 80 % of VO2max than at 60 % VO2max. Of the four recovery measurements investigated, EPOCMAG was the most sensitive to changes in exercise intensity and shows potential to reflect changes in the homeostatic stress of exercise at the group and individual level. Determining EPOCMAG may help to interpret the homeostatic stress of laboratory-based research trials or training sessions.