High-intensity aerobic interval training increases fat and carbohydrate metabolic capacities in human skeletal muscle.
High-intensity aerobic interval training (HIIT) is a compromise between time-consuming moderate-intensity training and sprint-interval training requiring all-out efforts. However, there are few data regarding the ability of HIIT to increase the capacities of fat and carbohydrate oxidation in skeletal muscle. Using untrained recreationally active individuals, we investigated skeletal muscle and whole-body metabolic adaptations that occurred following 6 weeks of HIIT (~1 h of 10 x 4 min intervals at ~90% of peak oxygen consumption (VO2 peak), separated by 2 min rest, 3 d.week-1). A VO2 peak test, a test to exhaustion (TE) at 90% of pre-training VO2 peak, and a 1 h cycle at 60% of pre-training VO2 peak were performed pre- and post-HIIT. Muscle biopsies were sampled during the TE at rest, after 5 min, and at exhaustion. Training power output increased by 21%, and VO2 peak increased by 9% following HIIT. Muscle adaptations at rest included the following: (i) increased cytochrome c oxidase IV content (18%) and maximal activities of the mitochondrial enzymes citrate synthase (26%), beta-hydroxyacyl-CoA dehydrogenase (29%), aspartate-amino transferase (26%), and pyruvate dehydrogenase (PDH; 21%); (ii) increased FAT/CD36, FABPpm, GLUT 4, and MCT 1 and 4 transport proteins (14%-30%); and (iii) increased glycogen content (59%). Major adaptations during exercise included the following: (i) reduced glycogenolysis, lactate accumulation, and substrate phosphorylation (0-5 min of TE); (ii) unchanged PDH activation (carbohydrate oxidation; 0-5 min of TE); (iii) ~2-fold greater time during the TE; and (iv) increased fat oxidation at 60% of pre-training VO2 peak. This study demonstrated that 18 h of repeated high-intensity exercise sessions over 6 weeks (3 d.week-1) is a powerful method to increase whole-body and skeletal muscle capacities to oxidize fat and carbohydrate in previously untrained individuals.
3 comments:
A good example of why Tabatas are over-rated by the crossfitters. To date, there are no good studies comparing one form of interval against another. Nor are there any studies at all that compare Tabatas (or whatever) against the same duration of moderate-high intensity without the rests. All of the interval studies are compared to longer duration of low-moderate intensity (really not pushing it). So yes, Tabatas work and so do these 4 min/2 min and so do equal time of going hard with no break. But nobody can say which is really best.
They are all good, and they all work. One can't do Tabatas all the time, as running that fast risks injury. But longer intervals = slower pace = less chance of injury.
I think this boils down to a case of define your goal(s), then choose the right tool to help achieve that goal. What energy system is it that you've identified as being lacking and/or do you want to improve? What phase of training are you in (i.e., GPP, etc.) Answering these questions will better direct one toward the correct interval ratio and frequency.
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