Next time you hear groans as you call out the start of another interval, remind everyone that when recovery breaks are too long, they undermine the effectiveness of high-intensity interval training. Researchers at Liverpool John Moores University in England compared fitness outcomes for participants in a 60HIIT protocol (six to 10 60–second intervals with 60-second rest breaks) with results for those in a 30HIIT protocol (four to eight 30–second intervals with 120-second rest breaks).

Subjects included 26 previously inactive adult men and women. Participants performed either of the two protocols for 6 weeks, three times a week. Investigators measured aerobic capacity, arterial stiffness and body composition. Data analysis showed improvements in aerobic capacity in the 60HIIT group members, but not the 30HIIT group. No differences occurred in any parameters with 30HIIT.

The study was presented at The Physiological Society’s conference, Future Physiology 2019: Translating Cellular Mechanisms into Lifelong Health Strategies, in December 2019.