Mechanisms of physiological changes need further study
The Burgomaster et al. paper said the validity of their findings on the doubling of endurance time to fatigue "is bolstered by the fact that all subjects performed extensive familiarization trials before testing and that a control group showed no change in endurance performance when tested 2 weeks apart with no sprint training intervention." In addition, though previous studies showed increases in citrate synthase (CS) activity and glycogen content after several weeks of sprint interval training with equivocal data, "we show here that the total training volume necessary to stimulate these metabolic adaptations is substantially lower than previously suggested."
Nevertheless, they note: "We can only speculate on potential mechanisms responsible for the dramatic improvement in cycle endurance capacity, but it is plausible that a training-induced increase in mitochondrial potential, as measured by CS maximal activity, improved respiratory control sensitivity during exercise as classically proposed (by J Holloszy and E. Coyle)?We hope that the present observations will stimulate additional research to clarify the precise nature, time course, and significance of the physiological adaptations induced by short sprint interval training."
The study, "Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans," by Kirsten A. Burgomaster, Scott C. Hughes, George J.F. Heigenhauser, Suzanne N. Bradwell and Martin J. Gibala, of McMaster University, Hamilton, Ontario, appears in the June issue of the Journal of Applied Physiology, published by the American Physiological Society. Except for Heigenhauser, researchers are with the Exercise Metabolism Research Group, Dept. of Kinesiology; H
Source:American Physiological Society