Maximal oxygen uptake (V̇O2max) may be considered the single most important predictor for long-distance endurance performance. Furthermore, such events are also influenced by other physiological factors involved in aerobic energy processes, that is, running economy (CR) and lactate threshold (LT), as well as a contribution from anaerobic metabolism. However, the capacity to produce energy derived from anaerobic sources is limited, and when whole-body performance persists more than 75s the majority of energy utilized originates from aerobic sources, a proportion which increases to ~90% when the event lasts ~10 min.
Given the great importance for long-distance endurance performance, a critical question is which training modality may yield the most potent V̇O2max improvements. Of duration, frequency and intensity, the latter is forwarded as particularly important to increase V̇O2max.
Aerobic high-intensity interval training (HIIT), applying intervals of 3–5 min, is one well-documented format to effectively improve V̇O2max in healthy individuals and various patient populations. The rationale for this design is that a high overload on oxygen transporting organs may only be achieved after 1–2 min because of delayed oxygen uptake, and that in theother end of the spectrum fatiguing processes sets an upper limit to the length of the interval, likely around 8–12 min.
Supramaximal sprint interval training (SIT) is another intermittent format that is advocated for effective improvements in V̇Ȯ2max and endurance performance. SIT is executed at high/maximal intensities. However, since fatigue occurs rapidly, the aerobic intensity is not necessarily accordingly high because of the sluggish oxygen uptake. Given the great importance of V̇O2max for long-distance endurance performance and health, studies investigating which interval training format may yield the largest increases in this crucial factor are warranted.
Forty-eight healthy non-smoking males (average 23 years) volunteered to participate in the present study. The subjects were aerobically well-trained and relatively accustomed to treadmill running, but not specializedrunners nor engaged in long-distance or sprint running competitions or trainings. They were randomized into three training groups: HIIT 4×4 min, SIT 8×20s, or SIT 10×30s. A V̇O2max above 50ml/kg/min and whole-body endurance training at least once per week were set as inclusion criteria.
Our main findings were that HIIT 4×4min increased V̇O2max more than the two SIT protocols. Furthermore, HIIT 4×4min enhanced long-distance endurance performance more than SIT 10×30s, while SIT 8×20s improvedanaerobic capacity more than HIIT 4 × 4 min.
Conclusion: HIIT 4×4min is superior for increasing V̇O2max compared withSIT protocols, carried out as 8 × 20 s and 10 × 30 s. Despite a lower overall intensity during HIIT 4×4 min than SIT, the aerobic intensity is higher during the former. HIIT should be the recommended interval formatfor aerobic performance.