Helgerud, J. Hov, H. Mehus, H. Balto, B. Boye, A. Finsås, L. Hoff, J. Wang, E.
Maximal oxygen uptake (VO2max) is widely acknowledged as a key physiological factor for endurance events involving large muscle mass, such as middle- and long-distance running. The last decades a myriad of training programs has emerged to effectively improve VO2max, with high-intensity intervals typically advocated to induce the largest increases. However, what may be the optimal interval format to improve VO2max is unclear, and sex-specific empirical evidence of training-induced responsesin females is scarce.
Interval training may be classified as aerobic high- intensity interval training (HIIT) or supramaximal sprint interval training (SIT). HIIT typically targets high aerobic intensity of about 90-95% of maximal heart rate, corresponding to about 95% of maximal aerobic speed (MAS), while SIT targets high overall intensity of about ≥150% of MAS.
The aim of the current study was to compare HIIT and SIT in aerobically well-trained females and contrast results to the recent findings in aerobically well-trained males following identical training protocols. Specifically, we compared one commonly applied HIIT protocol with two frequently used SIT protocols: (1) HIIT 4 × 4 min at ~95% of MAS interspersed by 3 min active recovery, (2) SIT 8×20s at ~150% of MAS interspersed by 10s passive recovery, (3) SIT; 10 × 30 s at ~175% of MAS interspersed by 3.5 min active recovery.
Only HIIT 4×4min exhibited an average 7.3% increase in VO2max and 8.4% increase in stroke volume of the heart (O2 pulse), and these increases were larger compared to both SIT protocols. In both SIT protocols no training-induced change in VȮ 2max and O2 pulse were observed.
Conclusion: HIIT improves VO2max more than SIT with both long and short recovery periods in aerobically well- trained females, while SIT improves sprint running performance (300m) more than HIIT. Treadmill running SIT 10 × 30 s induced an unacceptable rate of muscular strains, and it should therefore be carefully considered if applying this treadmill protocol is necessary
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