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A 2006 study (1) showed that brief, intense exercise training may induce metabolic and performance adaptations comparable to traditional endurance training. The study examined changes in exercise capacity and molecular and cellular adaptations in skeletal muscle after low volume sprint-interval training (HIT—high intensity training) and high volume endurance training (ET—traditional endurance training). Sixteen active men were assigned to a HIT or ET group (8 each) and performed six training sessions over 14 days. Each session consisted of either four to six repeats of 30 s ‘all out’ cycling at ~250% V02 peak with 4 min recovery (HIT) or 90–120 min continuous cycling at ~65% V02 peak (ET). The training time commitment over 2 weeks was 2.5 h for the HIT (high intensity) group  and 10.5 h for the ET group, and total training volume was 90% lower for SIT versus ET ( 630 versus 6500 kJ).

Even though the total training volume was significantly (i.e., 90%) lower for high intensity training test (HIT) subjects than versus traditional endurance training (ET) subjects, the study found that there was no performance difference between the HIT and ET groups.  Biopsy samples obtained before and after training revealed similar increases in muscle oxidative capacity, as reflected by the maximal activity of cytochrome c oxidase (COX) and COX subunits II and IV protein content (main effects, P ≤ 0.05), but COX II and IV mRNAs were unchanged. Training-induced increases in muscle buffering capacity and glycogen content were also similar between groups (main effects, P ≤ 0.05). Given the large difference in training volume, these data demonstrate that HIT is a time-efficient strategy to induce rapid adaptations in skeletal muscle and exercise performance that are comparable to ET in young active men.

(1). Martin J. Gibala, Jonathan P. Little, Martin van Essen, Geoffrey P. Wilkin,

Kirsten A. Burgomaster, Adeel Safdar, Sandeep Raha and Mark A. Tarnopolsky (Exercise Metabolism Research Group, Department of Kinesiology, McMaster University, Hamilton, Ontario, L8S 4K1, Canada; Departments of Pediatrics and Medicine, McMaster University, Hamilton, Ontario, L8N 3Z5, Canada), Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance, J Physiol  575.3 (2006) pp 901–911.

A 1996 study (2) showed that high-intensity intermittent training may improve both anaerobic and aerobic energy supplying systems significantly whereas moderate-intensity endurance training did not improve anaerobic capacity. The study showed that after the high-intensity training period, VO2max increased by 7 ml.kg-1.min-1, and anaerobic capacity increased by 28%.  On the other hand, the study showed that after six (6) weeks of moderate-intensity endurance training (intensity: 70% of maximal oxygen uptake (VO2max), 60 min.d-1, 5 d.wk-1), the anaerobic capacity did not increase significantly (P > 0.10), while VO2max increased from 53 +/- 5 ml.kg-1 min-1 to 58 +/- 3 ml.kg-1.min-1 (P < 0.01) (mean +/- SD).

The study authors proposed that the improvement probably resulted from imposing intensive stimuli on both the aerobic and anaerobic energy systems. The study consisted of two training experiments using a mechanically braked cycle ergometer. First, the effect of 6 wk of moderate-intensity endurance training (intensity: 70% of maximal oxygen uptake (VO2max), 60 min.d-1, 5 d.wk-1) on the anaerobic capacity (the maximal accumulated oxygen deficit) and VO2max was evaluated. After the training, the anaerobic capacity did not increase significantly (P > 0.10), while VO2max increased from 53 +/- 5 ml.kg-1 min-1 to 58 +/- 3 ml.kg-1.min-1 (P < 0.01) (mean +/- SD). Second, to quantify the effect of high-intensity intermittent training on energy release, seven subjects performed an intermittent training exercise 5 d.wk-1 for 6 wk. The exhaustive intermittent training consisted of seven to eight sets of 20-s exercise at an intensity of about 170% of VO2max with a 10-s rest between each bout. The study showed that after the high-intensity training period, VO2max increased by 7 ml.kg-1.min-1, and anaerobic capacity increased by 28%.  

(2). Tabata I, Nishimura K, Kouzaki M, Hirai Y, Ogita F, Miyachi M, Yamamoto K., Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max, Med Sci Sports Exerc. 1996 Oct;28 (10):1327-30.

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