REF-990 · Helgerud et al., 2007 · Medicine & Science in Sports & Exercise, Vol. · Paper · PubMed

Aerobic high-intensity intervals improve VO2max more than moderate training

B+moderate evidenceMeasured on recreational to trained athletesWritten before October 2026, being re-checked

In this randomized trial, aerobic endurance training of different intensities and methods was compared with total work and frequency matched.

Forty healthy, non-smoking, moderately trained men were allocated at random to four groups: long slow distance (70% HRmax), lactate threshold (85% HRmax), 15/15 interval running (15 s at 90-95% HRmax, 15 s of active rest at 70% HRmax), or 4 x 4 min interval running (4 min at 90-95% HRmax, 3 min of active rest at 70% HRmax).

Total oxygen consumption was similar across the four protocols, each done 3 days a week for 8 weeks. VO2max rose significantly more with high-intensity aerobic interval training than with long slow distance or lactate-threshold training (P < 0.01): by 5.5% in the 15/15 group and 7.2% in the 4 x 4 group.

After interval training, stroke volume went up by approximately 10% (P < 0.05).

Participants

n = 40: forty healthy, non-smoking, moderately trained male subjects, randomly assigned to four groups. Baseline VO2max 60.5 mL·kg-1·min-1 (15/15 group) and 55.5 mL·kg-1·min-1 (4 x 4 group); baselines of the other two groups, group sizes and age are not given in the abstract.

Protocol

Design: randomized, four parallel groups, matched for total work (similar total oxygen consumption) and frequency.
Groups: (1) long slow distance at 70% HRmax; (2) lactate threshold at 85% HRmax; (3) 15/15 — alternating 15 s runs at 90-95% HRmax with 15 s of active rest at 70% HRmax; (4) 4 x 4 min — 4-min runs at 90-95% HRmax, each followed by 3 min of active rest at 70% HRmax.
Dose: 3 days per week for 8 weeks.
Outcomes: VO2max, stroke volume of the heart, blood volume, lactate threshold, running economy.
Analysis: between-group comparison of the responses.

Key Results

High-intensity aerobic interval training increased VO2max significantly more than long slow distance and lactate-threshold training (P < 0.01).
15/15: VO2max +5.5%, from 60.5 to 64.4 mL·kg-1·min-1. 4 x 4 min: +7.2%, from 55.5 to 60.4 mL·kg-1·min-1.
Stroke volume increased significantly, by approximately 10%, after interval training (P < 0.05).
The abstract gives no VO2max figures for the long slow distance and lactate-threshold groups, and no results for blood volume, lactate threshold or running economy.
Authors' conclusion: high-aerobic-intensity interval training is significantly more effective than the same total work at lactate threshold or at 70% HRmax in improving VO2max; the VO2max changes correspond with the stroke-volume changes.

Practical Application

"At the same total work, does it matter for VO2max whether I run easy, at threshold, or do intervals?" In a randomized trial of 40 moderately trained men (four work-matched arms, 3 days a week for 8 weeks; between-group comparison), intervals at 90-95% HRmax raised VO2max by 5.5% (15/15) and 7.2% (4 x 4 min) — significantly more than long slow distance at 70% HRmax or threshold running at 85% HRmax (P < 0.01). In this population, intensity above threshold — not threshold work — was the stimulus that moved the ceiling.
Stroke volume rose by approximately 10% after interval training, which the authors link to the VO2max change.
Scope: men, moderately trained (baseline VO2max 55.5 and 60.5 mL·kg-1·min-1 in the two interval groups), 8 weeks. Inference, not tested here: transfer to women and to highly trained athletes.
The comparison is at EQUAL total work. Athletes do not usually swap easy running for intervals one-for-one; the trial does not test easy volume added on top.
The abstract reports no race or time-trial outcome and no threshold or economy result, so it shows the ceiling moved, not that performance did (see REF-989 for that gap in trained athletes).

Limitations

Forty men in four arms — small groups; group sizes are not given in the abstract.
The two interval groups started from different baselines (60.5 vs 55.5 mL·kg-1·min-1), so the 5.5% vs 7.2% contrast between formats is not a clean comparison.
Changes in the long slow distance and threshold groups are not reported numerically in the abstract.
Intensity was set by %HRmax, not by a measured threshold; "lactate threshold" training was defined as 85% HRmax.
No performance outcome in the abstract; 8 weeks only.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level

randomized, but 40 subjects spread over four arms; men only; VO2max and stroke volume outcomes, no performance test in the abstract

Content correction 2026-09-27
2026-10-02: aligned with the rewritten SYNTH-42 (missing stimulus, one lever per block, level C+): cross-reference description — "lever-to-stimulus mapping" -> "the starting bet".