Physiological responses to maximal 4 s sprint interval cycling using inertial loading: the influence of inter-sprint recovery duration.
Level 2 - randomized trial
Randomized crossover physiological trial in humans
PubMed 33974126 · doi:10.1007/s00421-021-04677-6
What was done
Sixteen young adults (8 females; age 23.5 ± 3.4 years; peak VO2 45.6 ± 9.2 ml·kg⁻¹·min⁻¹) completed three randomized trials consisting of 30 bouts of 4-second maximal cycling sprints on an Inertial Load Ergometer. The trials compared three different passive inter-sprint recovery intervals: 15, 30, and 45 seconds, assessing peak power output, oxygen consumption, heart rate, and perceived exertion.
What was found
Peak power output (PPO) remained stable across sprints with 30 s and 45 s recovery, though 45 s recovery produced 9% higher PPO than 30 s (p < 0.05). A 15 s recovery caused an 18% decline in PPO (p < 0.05) before stabilizing. The 15-, 30-, and 45-s trials elicited 72%, 56%, and 49% of VO2peak, and 86%, 80%, and 75% of maximal heart rate, respectively (all p < 0.001). Rating of perceived exertion ranged from 12.6 to 14.7 across conditions.
Why it matters
It characterizes the acute metabolic and mechanical trade-offs of micro-sprint protocols, showing that a 15-second rest substantially increases cardiovascular and aerobic demand at the expense of power output maintenance.
Limits
The sample size is small (n = 16) and restricted to healthy young adults. Only acute single-session responses were measured rather than long-term training adaptations. The trial was retrospectively registered.
Cited by
- supports Research by Dr. Edward Coyle investigated an interval protocol consisting of repeated 4-second all-out sprints interspersed with approximately 12 seconds of recovery.