Improvements in aerobic fitness but not mitochondrial content are intensity dependent in overweight men

The objective of this research was to determine the impact of the intensity of interval training on aerobic fitness, exercise performance, and skeletal muscle oxidative capacity in overweight young adults. 19 sedentary males (Age, 22.7 ± 3.9 yrs; BMI, 31.4 ± 2.6 kg/m 2 ; WC, 106.5 ± 6.6 cm) participated in 9 sessions of interval training at either 70% (LO) or 100% (HI) peak work rate over a three week period. Increases in VO 2 peak were greater (p<0.05) following HI (+27.9 ± 13.1%) than LO (+10.4 ± 22.0%) interval training. Performance on a time to completion trial also improved to a greater extent (p<0.05) following HI (+14.1 ± 4.3%) than LO (+8.6 ± 7.6%) training. Oxidative capacity improved in both groups with significant training effects (p<0.05) observed for COX I and COX IV protein content as well as citrate synthase maximal activity. βHAD maximal activity also tended to be higher following training (p = 0.07). No differences were observed between groups for any of the markers of oxidative capacity examined. These findings suggest that improvements in aerobic capacity and exercise performance may be sensitive to the intensity of interval training, while adaptations in skeletal muscle oxidative capacity may not. This research was supported by funding from NSERC.