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1 Exercise Metabolism Research Group, Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada L8S 4K1
2
Department of Physiology, University of Melbourne, Melbourne, Victoria, Australia 3010
Low-volume ‘sprint’ interval training (SIT) stimulates rapid improvements in muscle oxidative capacity that are comparable to levels reached following traditional endurance training (ET) but no study has examined metabolic adaptations during exercise after these different training strategies. We hypothesized that SIT and ET would induce similar adaptations in markers of skeletal muscle carbohydrate (CHO) and lipid metabolism and metabolic control during exercise despite large differences in training volume and time commitment. Active but untrained subjects (23 ± 1 years) performed a constant-load cycling challenge (1 h at 65% of peak oxygen uptake 
before and after 6 weeks of either SIT or ET (n = 5 men and 5 women per group). SIT consisted of four to six repeats of a 30 s ‘all out’ Wingate Test (mean power output 
500 W) with 4.5 min recovery between repeats, 3 days per week. ET consisted of 40–60 min of continuous cycling at a workload that elicited 65% 
(mean power output 150 W) per day, 5 days per week. Weekly time commitment (1.5 versus 4.5 h) and total training volume (225 versus 2250 kJ week–1) were substantially lower in SIT versus ET. Despite these differences, both protocols induced similar increases (P < 0.05) in mitochondrial markers for skeletal muscle CHO (pyruvate dehydrogenase E1
protein content) and lipid oxidation (3-hydroxyacyl CoA dehydrogenase maximal activity) and protein content of peroxisome proliferator-activated receptor-
coactivator-1. Glycogen and phosphocreatine utilization during exercise were reduced after training, and calculated rates of whole-body CHO and lipid oxidation were decreased and increased, respectively, with no differences between groups (all main effects, P < 0.05). Given the markedly lower training volume in the SIT group, these data suggest that high-intensity interval training is a time-efficient strategy to increase skeletal muscle oxidative capacity and induce specific metabolic adaptations during exercise that are comparable to traditional ET.
(Received 1 August 2007;
accepted after revision 23 October 2007;
first published online 8 November 2007)
Corresponding author M. J. Gibala: Exercise Metabolism Research Group, Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada L8S 4K1. Email: gibalam{at}mcmaster.ca
Related Article
J. Physiol. 2008 586: 1-2.
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  J. A. Hawley Specificity of training adaptation: time for a rethink? J. Physiol., January 1, 2008; 586(1): 1 - 2. [Full Text] [PDF]
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