REF-1446 · Moran-MacDonald et al., 2026 · European Journal of Applied Physiology, online 6 August · Paper · PubMed

Does adding easy riding to 3 interval sessions help?

6 weeks, 19 moderately trained riders, one arm adding 4 h/week in the moderate domain: no detectable gain in time trial, peak power or thresholds. Underpowered, short; abstract only.

Main caveat: Abstract only; closed access. HIIT protocol and most numbers missing.
limited evidenceMeasured on trained athletes

Moran-MacDonald and colleagues (Queen's University, Canada) separated the two parts of a polarized week. Nineteen cyclists and triathletes (17 men) did HIIT on 3 days a week for 6 weeks, with (POL) or without (HIIT) an additional 240 min a week of cycling in the moderate intensity domain.

Time trial, peak work rate and lactate thresholds (LT1, LT2) were tested before and after, and peak work rate and thresholds were retested at week 3 to re-set intensities. Both groups reduced time-trial time by an average of 8.5 ± 1.2%. No time × group interaction appeared for any outcome, despite about 23 more hours of training in POL.

An exploratory analysis found that the observed between-group effect (η² printed as 0.4, called modest) would need more than 100 participants per group for significance. The authors conclude that adding moderate training to HIIT does not bring further gains over 6 weeks and that gains "appear to be driven primarily by the Severe-intensity component".

Our reading: the cleanest controlled test in the base of "add easy hours to the intervals" in trained amateurs, and it fits SYNTH-51's house line that quality sessions carry the adaptation when time is short.

It cannot show the extra hours are worthless: 6 weeks with about 10 per arm is short and small, there was no easy-only comparator so "driven by the severe component" is the authors' inference, and durability was not measured (REF-1100, B, in elite riders, found a preloaded time trial did not improve significantly overall).

Protocol

Participants: n = 19 cyclists and triathletes (17 men), moderately trained; randomly allocated (arm sizes not in the abstract).
Training: 3 days a week of HIIT in both arms; POL added 240 min a week in the moderate domain; 6 weeks; intensities re-set at week 3.
Outcomes: time trial (distance not stated), peak work rate, LT1, LT2.
Not in the abstract: HIIT protocol, group means for peak work rate and thresholds, adherence, CIs.
Funding and interests (as printed): National Science and Engineering Research Council of Canada, grant 402635; the authors have no competing interests to declare.

Key Results

Outcome after 6 weeksHIIT onlyHIIT + 240 min/week moderateBetween groups
Time-trial timereducedreducedboth 8.5 ± 1.2% on average; no time × group interaction
Peak work ratenot givennot givenno time × group interaction
LT1, LT2not givennot givenno time × group interaction
Extra trainingnoneabout 23 h over 6 weeksperformed, per the abstract (240 min a week for 6 weeks would be 24 h, our arithmetic)
Power: the authors estimate more than 100 participants per group for the observed effect (exploratory).
Individual response: not reported in the abstract.

Mechanisms

Measured: similar gains with or without four added easy hours a week over 6 weeks.
Authors' interpretation: the severe-intensity component drives gains in moderately trained athletes over this period.
Inference: a large shared gain (8.5%) from three interval days can leave little room to detect a further effect, and easy volume may pay over longer spans or on outcomes not tested here.

Practical Application

Does adding easy riding to 3 interval sessions help? 6 weeks, 19 moderately trained riders, one arm adding 4 h/week in the moderate domain: no detectable gain in time trial, peak power or thresholds. Underpowered, short; abstract only.
Time-limited rider: this is a direct but underpowered test, and it gives no reason to treat easy hours as obligatory in a short block, in line with SYNTH-26's and SYNTH-51's practice. Not from this paper; the base's own practice: three interval days are not the default for most amateurs, whose week holds about two quality sessions (SYNTH-26).
What it does not show: that easy riding has no value (6 weeks; no durability, no season), that three HIIT days are sustainable, or anything about tempo or between-threshold work as the added session.

Limitations

Abstract only; closed access. HIIT protocol and most numbers missing.
Small and underpowered by the authors' own estimate; a null is not equivalence.
Short (6 weeks); volume effects may need longer.
No easy-only arm, so the attribution to the severe component is inference.
The printed η² of 0.4 is called modest, which does not match the usual reading of that statistic; not checkable from the abstract.
Mostly men (17 of 19).
Funding: public research council; no competing interests declared.
How this entry was checked and changed
Why this level

(from the abstract) — the rubric's B for a parallel RCT under 20; registration and a performance outcome count in its favour, but the arm sizes, HIIT protocol, time-trial distance and group numbers are not in the abstract, and the trial is underpowered by its authors' estimate