Aerobic high-intensity intervals are superior to improve (V)over dotO2max compared with sprint intervals in well-trained men

Maximal oxygen uptake ((V)over dotO(2max)) may be the single most important factor for long-distance running performance. Interval training, enabling high intensity, is forwarded as the format that yields the largest increase in (V)over dotO(2max). However, it is uncertain if an optimal outcome on (V)over dotO(2max), anaerobic capacity, and running performance is provided by training with a high aerobic intensity or high overall intensity. Thus, we randomized 48 aerobically well-trained men (23 +/- 3 years) to three commonly applied interval protocols, one with high aerobic intensity (HILT) and two with high absolute intensity (sprint interval training; SIT), 3x week for 8 weeks: (1) HIIT: 4 x 4 min at similar to 95% maximal aerobic speed (MAS) with 3 min active breaks. (2) SIT: 8 x 20 s at similar to 150% MAS with 10 s passive breaks. (3) SIT: 10x 30s at similar to 175% MAS with 3.5 min active breaks. (V)over dotO(2max) increased more (p<0.001) following HIIT, 4 x 4 min (6.5 +/- 2.4%, p<0.001) than SIT, 8 x 20s (3.3 +/- 2.4%, p <0.001) and SIT, 10 x 30s (n.s.). This was accompanied by a larger (p<0.05) increase in stroke volume (O-2-pulse) following HIIT, 4 x 4 min (8.1 +/- 4.1%, p<0.001) compared with SIT, 8 x 20 s (3.8 +/- 4.2%, p < 0.01) and SIT, 10 x 30 (n.s.). Anaerobic capacity (maximal accumulated oxygen deficit) increased following SIT, 8 x 20 s (p < 0.05), but not after HIIT, 4 x 4 min, nor SIT, 10 x 30 s. Long-distance (3000-m) endurance performance increased (p <0.05-p <0.001) in all groups (MIT, 4 x 4 min: 5.9 +/- 3.2%; SIT, 8 x 20 s: 4.1 +/- 3.7%; SIT, 10x 30s: 2.2 +/- 2.2%), with HIIT increasing more than SIT, 10 x 30 s (p < 0.05). Sprint (300-m) performance exhibited within-group increases in SIT, 8 x 20 s (4.4 +/- 2.0%) and SIT, 10 x30 s (3.3 +/- 2.8%). In conclusion, HIIT improves (V)over dotO(2max) more than SIT. Given the importance of (V)over dotO(2max) for most endurance performance scenarios, HIIT should typically be the chosen interval format.

Automated summary

This study compared high aerobic intensity interval training (HIIT) with high overall intensity interval training (SIT) and found that HIIT had a greater improvement on maximal oxygen uptake ((V)over dotO(2max)). It also improved long-distance running endurance and sprint performance.