REF-705 · Guimarães, Foresti, Papoti & Azevedo, 2026 · Journal of Strength & Conditioning Research, · Paper · PubMed
Easy sessions run AT the first threshold (the top of the moderate domain) gave the same 6-week gains as running 10-15% below it
With a somewhat higher psychophysiological load that stayed within acceptable limits
Participants
n=20 trained amateur runners, divided into 2 groups of 10 (6 men and 4 women in each).
Protocol
12-week study: 4 weeks of familiarisation with the tests and training, then 6 weeks of intervention. Training was volume-equated between groups; the only prescribed difference was the intensity of the low-intensity sessions:
| Group | Low-intensity sessions run at |
|---|---|
| VL1 | the upper limit of the moderate domain (first threshold) |
| Below-VL1 | 10-15% below that limit |
Outcomes: body composition, neuromuscular adaptations and performance (pre/post); training and recovery sessions monitored for psychophysiological factors.
Full text; not checked against the abstract: 5 sessions/week — 3 low-intensity (45-60 min), 1 medium-intensity (between the thresholds), 1 high-intensity (intervals above the second threshold), ~47 km / ~4.5 h per week; performance measured as critical speed and a 3600 m time trial; monitoring included session RPE of the easy sessions and morning perceived fatigue.
Key Findings
| Outcome | VL1 vs 10-15% below |
|---|---|
| Neuromuscular variables | no between-group difference; both improved pre → post |
| Performance | no between-group difference; both improved pre → post |
| D′ (finite work capacity above critical speed) | worsened in both groups |
| Psychophysiological variables (session/recovery monitoring) | differed between groups at some time points, higher for VL1, but within acceptable limits |
Intensity placement inside the moderate domain was not a dose lever for adaptation. Sitting at the first threshold bought nothing measurable over six weeks; the psychophysiological cost was somewhat higher at times, not a large or sustained divergence.
The authors' conclusion: in trained amateur runners, neuromuscular variables and performance improve similarly whether training sits at the top of the moderate domain or 10-15% under it.
Full text; not checked against the abstract: the separation in perceived fatigue appeared around week 3, while performance never separated.
Practical Application
In n=20 trained amateur runners (6M/4W per group) training volume-equated for 6 weeks with easy sessions either at the first threshold or 10-15% below it, neuromuscular and performance gains were the same in both groups (D′ worsened in both), and the only difference was a psychophysiological load that was higher for the at-threshold group at some time points, within acceptable limits — pinning easy runs to the top of the moderate domain did not buy extra adaptation.
Prescribe easy sessions comfortably below the first threshold, not pinned to it. "As close to LT1/VT1 as you can hold" is not a better easy session; over six weeks it produced the same adaptation at a slightly higher perceived cost.
On easy days the lever for more adaptation is DURATION and frequency, not proximity to threshold (inference from the volume-equated design: the same volume gave the same result regardless of placement within the zone).
Reading a completed easy session: drifting up toward threshold is not a bonus. An easy ride executed at LT1 should not be graded as better-executed than one at 10-15% below it.
Inference, not tested: if easy-day HR/power is creeping toward the first threshold while fatigue climbs and performance stays flat, bringing the easy sessions down 10-15% is the cheapest first adjustment. This study did not test that intervention; it compared two fixed prescriptions.
Monitoring: subjective psychophysiological measures were where the two groups differed at all, and performance never did (REF-368 reaches the same conclusion about subjective measures generally).
Limitations
n=20 (10 per group, mixed sex), six weeks, trained amateurs. Small and short. A 15-20 h/week athlete's easy-day economics are not established here (the fatigue argument plausibly strengthens with volume, but that is inference).
Running only. There is no cycling data in this study. The popular framing of this result as a "zone 2 riding" finding is an extrapolation, not a measurement.
Only VL1 versus −10-15% was tested. Whether −20% or −30% would give the same adaptation is unknown, so this does not license "the easier the better" — no minimum effective intensity has been established.
D′ worsened in both groups, so the programme as a whole did not protect anaerobic capacity; neither easy-day prescription fixes that.
The psychophysiological difference was intermittent ("at some times") and within acceptable limits — the abstract does not support a claim of meaningful accumulated fatigue.
Weekly structure, volume and the specific performance tests come from the full text and were not checked against the abstract.
How this entry was checked and changed
Content correction 2026-09-27
"Fatigue lever", "the fatigue was not the same", "more accumulated fatigue" -> psychophysiological variables were higher for the VL1 group at some time points but within acceptable limits; softened throughout.
Added: 6 men + 4 women per group; 4-week familiarisation before the 6-week intervention; D′ worsened in both groups; volume-equated design.
"Morning perceived fatigue from week 3" and the weekly structure / critical speed / 3600 m details -> marked as full text, not checked against the abstract. The "bring easy sessions down 10-15%" bullet -> labelled inference, not tested. Journal line: now published 40(10), not ahead of print.