Two weeks of high-intensity aerobic interval training increases the capacity for fat oxidation during exercise in women

1 Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada, 2 Department of Sport Studies, University of Stirling, Stirling, Scotland; and 3 Department of Medicine, McMaster University, Hamilton, Ontario, Canada Submitted 26 September 2006 ; accepted in final form 7 December 2006 Our aim was to examine the effects of seven high-intensity aerobic interval training (HIIT) sessions over 2 wk on skeletal muscle fuel content, mitochondrial enzyme activities, fatty acid transport proteins, peak O 2 consumption ( O 2 peak ), and whole body metabolic, hormonal, and cardiovascular responses to exercise. Eight women (22.1 ± 0.2 yr old, 65.0 ± 2.2 kg body wt, 2.36 ± 0.24 l/min O 2 peak ) performed a O 2 peak test and a 60-min cycling trial at 60% O 2 peak before and after training. Each session consisted of ten 4-min bouts at 90% O 2 peak with 2 min of rest between intervals. Training increased O 2 peak by 13%. After HIIT, plasma epinephrine and heart rate were lower during the final 30 min of the 60-min cycling trial at 60% pretraining O 2 peak . Exercise whole body fat oxidation increased by 36% (from 15.0 ± 2.4 to 20.4 ± 2.5 g) after HIIT. Resting muscle glycogen and triacylglycerol contents were unaffected by HIIT, but net glycogen use was reduced during the posttraining 60-min cycling trial. HIIT significantly increased muscle mitochondrial -hydroxyacyl-CoA dehydrogenase (15.44 ± 1.57 and 20.35 ± 1.40 mmol·min –1 ·kg wet mass –1 before and after training, respectively) and citrate synthase (24.45 ± 1.89 and 29.31 ± 1.64 mmol·min –1 ·kg wet mass –1 before and after training, respectively) maximal activities by 32% and 20%, while cytoplasmic hormone-sensitive lipase protein content was not significantly increased. Total muscle plasma membrane fatty acid-binding protein content increased significantly (25%), whereas fatty acid translocase/CD36 content was unaffected after HIIT. In summary, seven sessions of HIIT over 2 wk induced marked increases in whole body and skeletal muscle capacity for fatty acid oxidation during exercise in moderately active women. fatty acid metabolism; mitochondrial enzymes; aerobic capacity; fatty acid transport Address for reprint requests and other correspondence: J. L. Talanian, Dept. of Human Health and Nutritional Sciences, Univ. of Guelph, Guelph, ON, Canada N1G 2W1 (e-mail: jtalania{at}uoguelph.ca )