REF-036 · Inglis et al., 2024 · Medicine & Science in Sports & Exercise, Vol. · Paper

Heavy/Severe/Extreme intensity increase VO2max; Moderate does NOT

A-fairly strong evidenceMeasured on recreational to trained athletesWritten before October 2026, being re-checked

Participants

n=84 young healthy participants (42 females, 42 males), randomly assigned to six age-, sex- and VO2max-matched groups of 14.

Protocol

Randomised parallel design: eighty-four young healthy participants (42 females, 42 males) assigned to six age-, sex- and VO2max-matched groups of 14 (from the abstract)
Continuous cycling in the moderate, lower heavy or upper heavy domain; HIIT in the severe domain; sprint-interval training (SIT) in the extreme domain; or no exercise (control); all training groups except SIT were work-matched
Three sessions per week for 6 weeks, with physiological evaluations at PRE, MID and POST
Measures: change in VO2max, and change in power output at the estimated lactate threshold and at maximal metabolic steady state

6 Groups (6 weeks, 3 sessions/week, cycling)

1

MOD (continuous, moderate domain)

2

HVY1 (continuous, lower heavy domain)

3

HVY2 (continuous, upper heavy domain)

4

HIIT (intervals, severe domain)

5

SIT (sprint intervals, extreme domain)

6

CON (no exercise)

All training groups except SIT were work-matched. Testing at PRE, MID and POST.

Results — change in VO2max (mL·kg⁻¹·min⁻¹)

GroupΔ VO2maxSignificant vs control?
CON+0.1 ± 1.2—
MOD+1.8 ± 2.7NO (P > 0.05)
HVY1+3.3 ± 2.4Yes
SIT+4.7 ± 2.3Yes
HVY2+5.4 ± 2.3Yes
HIIT+6.2 ± 2.8Yes (largest increase)

Thresholds: the change in power at the estimated lactate threshold (θLT) was similar across HVY1, HVY2, HIIT and SIT and greater than CON in all four (P < 0.05); for MOD it was not different from CON. HIIT produced the largest gain in power at maximal metabolic steady state, greater than CON, MOD and SIT (P < 0.05).

Critical Conclusion

Moderate-domain continuous training (below the first threshold) did not raise VO2max or the lactate threshold beyond control in these young healthy participants over 6 weeks. Every intensity from the heavy domain upward did. HIIT (severe domain) produced the largest VO2max gain and the largest gain at maximal metabolic steady state.

Practical Application

In 84 young healthy adults training 3×/week for 6 weeks, only groups working in the heavy domain or above raised VO2max beyond control (HIIT +6.2, HVY2 +5.4, SIT +4.7, HVY1 +3.3 mL·kg⁻¹·min⁻¹); moderate-domain continuous training (+1.8) did not — a block that must move VO2max needs work at or above the heavy domain, with severe-domain intervals giving the largest gain here.
Inference, not tested: raising FTP eventually runs into the VO2max ceiling, so a VO2max-directed block belongs in the plan; this study does not itself test FTP progression or trained athletes.
Domain-based prescription (relative to the individual's thresholds) gave a homogeneous stimulus across participants — the authors' second conclusion.

Limitations

Young healthy participants of unstated training status; 6 weeks; the moderate group's null may not hold over longer periods or in different populations.
Group means with 14 per group; within-group variability is large (SDs of 2.3-2.8 mL·kg⁻¹·min⁻¹).
How this entry was checked and changed
Why this level

regraded 2026-09-27 from A: parallel RCT, n=84 (14 per group), not pre-registered/≥100

Content correction 2026-09-27
Table values corrected to the abstract: HVY1 +3.0 ± 2.4 -> +3.3 ± 2.4; HVY2 +4.2 ± 3.1 -> +5.4 ± 2.3; HIIT ± 3.5 -> ± 2.8; SIT +5.1 ± 2.9 -> +4.7 ± 2.3 (order of effect is HIIT > HVY2 > SIT > HVY1).
Added the threshold results from the abstract; the FTP remark is now labelled inference.
Tier: "recreationally active/trained" -> Tier 1-2 (abstract says young healthy, no training status). Level A -> A- (parallel RCT, n=84).
2026-09-28: added Protocol from the abstract (Europe PMC/PubMed PMID 38376995).
2026-09-28: journal issue/pages corrected from the DOI's Crossref record (56(8), 1476-1488 -> 56(7), 1307-1316).