REF-1049 · Seiler & Sjursen, 2004 · Scandinavian Journal of Medicine & Science in Sports, · Paper · PubMed
Self-paced intervals with 1:1 rest ended at the same RPE (about 17) and lactate (about 4.5 mmol/L) whether the reps were 1, 2, 4 or 6 minutes
But 1-minute reps reached only 82% of VO2max against about 92% for 2–6-minute reps
Key Findings
Peak VO2 averaged about 92 ± 4% of VO2max for 2-, 4- and 6-minute intervals against 82 ± 5% for 1-minute bouts (P < 0.001).
Twelve well-trained runners (9 men, 3 women, VO2max 65 ± 6) ran 24 × 1, 12 × 2, 6 × 4 and 4 × 6 minutes at a self-selected hard pace with a 1:1 work-to-rest ratio — 24 minutes of work in every session.
Running velocity fell as the reps lengthened: 93%, 88%, 86% and 84% of the velocity at VO2max.
Peak RPE was about 17 ± 1 in all four sessions and lactate was similar (4.3–4.6 mmol/L).
The authors conclude that the optimal duration for a high physiological load is 3–5 minutes under these conditions.
Practical Application
With equal rest, short reps are an easier session, not a better one: 1-minute on, 1-minute off leaves oxygen uptake well short of what 2–6-minute reps reach, at the same perceived effort.
For time near VO2max with a 1:1 structure, use reps of about 3–5 minutes. Short reps only become a VO2max session when the rest is short and active REF-1051.
Limitations
Acute and self-paced, so rep length is confounded with the speed chosen; running; time above 90% VO2max is not in the abstract (abstract only was read).
Rest length mattered little in a companion study: 1, 2 or 4 minutes of rest had limited impact on 6 × 4 minutes (Seiler & Hetlelid 2005, DOI 10.1249/01.mss.0000177560.18014.d8).