Which interval training protocol increases VO2 max the most?
Long-interval training with blocks of at least 2 minutes, sufficient volume per session, and a programme of at least 4 weeks produces the greatest VO2 max gains. Short all-out sprints take less time but do not deliver greater gains.
Long-interval training has the strongest support when it comes to increasing VO2 max (your body's maximum oxygen uptake). Work intervals of at least 2 minutes, at least 15 minutes of active work per session, and a programme lasting at least 4 weeks produce the greatest improvement. This protocol demonstrably outperforms shorter intervals and also beats standard endurance training.
Sprints of 30 seconds or less (sometimes called all-out sprint interval training) are considerably more time-efficient and increase VO2 max by an average of 4 to 13 percent over 2 to 8 weeks. However, they are no better than standard continuous endurance training when it comes purely to VO2 max gains. The advantage lies in the shorter time investment, not in a greater training effect.
Interval training produces slightly larger VO2 max gains in healthy adults than endurance training, but the difference is small: on average around 1.2 mL/kg/min extra. People who start with a lower fitness level benefit more. Longer programmes of more than 8 weeks consistently produce greater gains, both in VO2 max and in muscle strength.
How long the rest periods between intervals are makes no clear difference according to several analyses. What does matter is the duration of the work intervals (longer is better), the total volume per session, and the length of the programme. Anyone wanting maximum VO2 max growth should therefore choose longer blocks of work at high intensity, not the shortest all-out sprints.
This answer draws on eight large reviews that each bring together dozens of studies, including research in healthy adults, students, young athletes, and basketball players. The evidence that long-interval high-intensity training is the best protocol is the strongest and most consistent. The evidence for sprint interval training is also solid, but comparisons with endurance training show no clear advantage. The researchers behind the study on young athletes note that only 1 in 10 participants was female, so those findings apply mainly to boys.