Influence of recovery duration during 6-s sprint interval exercise on time spent at high rates of oxygen uptake

This study examined whether time spent at high rates of oxygen consumption (VO₂) during 6-s sprint interval exercises (SIE) is a function of recovery interval duration. In a randomised crossover study, thirteen male endurance runners performed 40 × 6-s all-out sprints interspersed with 15-s, 30-s and 60-s passive recovery intervals (SIE₁₅, SIE₃₀, and SIE₆₀ trials respectively), and a work duration-matched Wingate-SIE (8 × 30-s all-out sprints with 4-min passive recovery, SIE_Win trial). The accumulated exercise time at ≥ 80%, 85%, 90%, 95% and 100% of VO_2max, and maximum heart rate (HR_max) in the four trials were compared. During the 6-s SIEs, accumulated time spent at all selected high rates of VO_2max increased as recovery time decreased, whilst the SIE work rate decreased (p <.05). In SIE_Win, although the exercise lasted longer, the time spent at ≥90% VO_2max (74 ± 16 s) was significant less than that in SIE₁₅ (368 ± 63 s, p <.05), yet comparable to that in SIE₃₀ (118 ± 30 s, p >.05), and longer than that in SIE₆₀ (20 ± 14 s, p <.05). The differences between the four trials in accumulated time at high percentages of HR_max were similar to those for VO₂, although the temporal characteristics of the increases in HR and VO₂ during the SIEs were different. In conclusion, the duration of the recovery interval in 6-s SIE protocols appears to be a crucial parameter when sprint interval training is prescribed to enhance aerobic capacity. Further, the SIE₁₅ protocol may represent a potential alternative to 30-s SIE_Win in the development of time-efficient aerobic training intervention.