REF-140 · Matomäki, 2025 · European Journal of Applied Physiology, Vol. · Paper

Why low-intensity endurance training for athletes?

C+thin evidenceMeasured on a mixed groupWritten before October 2026, being re-checked

Central Paradox

Endurance athletes spend most of their training in the low-intensity zone. At first sight that makes little sense: in the short term, easy exercise does not stress homeostasis or the cardiopulmonary system of high-level athletes enough to yield performance gains on a par with moderate- or high-intensity work. Why do they do it?

Key Findings — 7 hypotheses (not mutually exclusive)

The abstract gives the span of the hypotheses: at one end, a psychological need for easy days, plus the added gains easy training brings without piling up stress; at the other, the possibility that this kind of training could in the end be replaced. The individual headings below follow the paper (full text, checked 2026-09-27):

1

Psychological need for easy days — mental recovery, lower cognitive stress in a high-frequency training week.

2

Incremental benefit without stress accumulation — small, cumulative aerobic gains that do not add muscle damage or metabolic stress and so do not interfere with recovery.

3

Adaptation maintenance and recovery between hard sessions — low-intensity work as maintenance of existing aerobic adaptations and as active recovery.

4

Mitochondrial signalling through volume — weak per-session signalling that accumulates with large volume.

5

Fat-metabolism adaptation — long low-intensity sessions as the stimulus for fat oxidation and glycogen sparing.

6

Structural adaptations — connective tissue, tendon and bone tolerance built with low injury risk.

7

Low-intensity training may be replaceable — the provocative hypothesis: some of the volume may be substitutable without loss of adaptation (see the author's microinterval experiment, REF-134).

No hypothesis is tested in this paper; no numbers are given in the abstract.

Practical Application

Perspective paper, no data: seven non-exclusive explanations are proposed for why endurance athletes spend most of their training at low intensity — from a psychological need for easy days and incremental gains without accumulated stress, to the possibility that low-intensity training may ultimately be replaceable. Treat the high-volume/low-intensity habit as a practice with several plausible rationales, none of them proven by this paper.
Not from this paper; the base's own practice: keep the long low-intensity sessions in base phases for fat-oxidation and durability reasons, and consider replacing a portion of easy volume with microintervals (REF-134) when a neuromuscular stimulus is wanted without added metabolic load.
Inference, not tested: if hypotheses 2-3 are the main drivers, the value of easy volume shows up as recovery quality and consistency across weeks rather than as a measurable per-session gain.

Limitations

Perspective paper — no new experimental data, single author. Seven hypotheses of unequal support; hypothesis 7 (replaceability) is explicitly provocative and requires longitudinal research. The headings beyond those named in the abstract come from the full text and were not checked here.

How this entry was checked and changed
Why this level

regraded 2026-09-27 from B+: single-author perspective proposing hypotheses, no systematic method, no data

Content correction 2026-09-27
Level B+ -> C+: single-author perspective, no systematic method.
"~80% training time", "10-13 sessions/week", "3-5h long sessions", "FatMax" -> not in the abstract; deleted or relabelled base practice.
Hypothesis headings 3-6 -> labelled full text; not checked against the abstract (abstract names only the first two and the last).
"Justification for 80% Z1 distribution" -> reframed: the paper explains a practice, it does not justify a percentage.
Lines labelled "full text; not checked" were read against the open-access full text (PMC12423243): 1 confirmed and relabelled.