Abstract 3888: Exercise-induced Increase in Cardiac Efficiency: The Impact of Intensity
There is growing evidence that exercise has beneficial effects in patients with cardiovascular disease. Although the importance of the intensity, duration and modality of the exercise training is debated, recent studies have indicated more beneficial cardiovascular effects of high- as compared to low- and moderate-intensity levels. The significance of exercise intensity with respect to myocardial substrate metabolism, oxygen consumption (MVO2) and cardiac efficiency is, however, not known. Thus, the aim of the study was to compare cardiometabolic effects of high-intensity interval training (HIT) vs. moderate-intensity continuous training (MIT). Male C57BL/6J mice were subjected to high-intensity (85–95% of VO2max) interval treadmill running or moderate-intensity (50 –70% of VO2max) continuous running for 10 wks (5 days/wk), as described by Kemi et al. (J Applied Physiol, 2002), both groups covering the same running distance. Age-matched sedate mice served as controls. Myocardial substrate utilization (radioisotope technique), cardiac efficiency (regression analysis of cardiac work -MVO2 relationships) and the oxygen cost for basal metabolism and E-C coupling were measured in isolated perfused hearts. HIT increased max running speed by 60%, which was accompanied with an 18% increase in aerobic capacity (VO2max). The corresponding numbers for MIT were 30% and 10%. Both modes of exercise were associated with a 10% increase in heart weight to body weight ratio, but altered cardiac substrate utilization was observed only in the HIT group, as revealed by a 36% increase in glucose oxidation and a concomitant reduction in fatty acid oxidation. In addition, only HIT significantly increased cardiac efficiency, due to a decrease in the oxygen cost for basal metabolism. In conclusion, high, but not moderate intensity training was associated with a shift in myocardial substrate utilization in favour of glucose oxidation, combined with increased cardiac efficiency. Improvement of cardiac metabolism and efficiency may in part explain the superiority of high-intensity exercise training with regard to cardioprotection in patients with cardiovascular disease, an issue that should be followed up with further investigations.