REF-1247 · Viru et al., 2001 · European Journal of Applied Physiology · Paper · PubMed

Do bigger cortisol and growth-hormone rises mean better durability?

Not shown. In 12 athletes split 6/6 after the fact, 1-min power rose after a 2-h run in the 6 whose cortisol rose, fell in the rest. One small study, 2001, abstract.

B-limited, mixed evidenceMeasured on trained to highly trained athletes

Viru et al. asked whether fatigue changes the hormone responses to exercise. Twelve endurance-trained athletes did a 10-min test at 70% of maximal oxygen uptake (1st test), ran for 2 h at an intensity that gave a blood lactate of about 2 mmol/l, and repeated the 10-min test (2nd test); a 1-min anaerobic power test measured muscle power before and after the run.

Cortisol, growth hormone (GH), testosterone and insulin were measured before and after each 10-min test. Fresh, the test raised cortisol and GH (P < 0.05), lowered insulin (P < 0.01) and left testosterone unchanged.

The run lowered insulin, raised GH and moved cortisol and testosterone variably; after the run the test lowered insulin further (P < 0.05), while cortisol, GH and testosterone responses varied between athletes.

Split by cortisol, 6 athletes (group A) showed a rise from baseline of 304.0 (SD 60.0) nmol/l and 6 (group B) a decrease or no change, +3.1 (5.3) nmol/l; following the 2nd test GH had risen 14.7 (4.8) ng/ml in group A against 6.0 (2.9) in group B; and 1-min anaerobic power was higher after the run than before it in group A and lower in group B (P < 0.05).

The authors suggest that the fatigue of a long endurance bout may reset the pituitary-adrenocortical system, intensifying its responses in some athletes and suppressing them in others. Our reading: a small, uncontrolled study whose groups were defined by the hormone being compared.

It shows that the endocrine response to a standard effort after a long run differs widely between athletes, and hints that those whose cortisol response was suppressed also lost short-effort power.

It does not measure durability as the base uses the word (REF-195: the onset and size of the deterioration during prolonged exercise), gives no size for the power changes in the abstract, and cannot say whether the hormones caused anything.

A newsletter summary (October 2026) presented it as evidence that larger cortisol and GH rises go with better durability; Limitations lists where that goes beyond the paper.

Protocol

Design (from the abstract): within-subject pre-post experiment in one fixed order, with no control condition (no repeat of the tests without the run); the participants were divided afterwards into two groups by their cortisol response.
Who: n = 12 endurance-trained athletes; men per the MEDLINE indexing (MeSH Male; the abstract says "athletes"). Sport, age, VO2max and training are not given in the abstract.
Fatiguing bout: a 2-h run at an intensity giving a blood lactate concentration of about 2 mmol/l. How the speed was set, the surface or treadmill, and fluid and carbohydrate intake are not given.
Hormone-responsiveness tests: 10 min at 70% of maximal oxygen uptake before (1st test) and after (2nd test) the run; the mode (running or ergometer) is not given.
Muscle power: a 1-min anaerobic power test, compared before vs after the run; its mode, its timing relative to the 10-min tests and the power values are not given in the abstract. The newsletter summary describes it as a 1-min all-out cycling test; not checked.
Blood: cortisol, GH, testosterone and insulin before and after the 1st and the 2nd test.
Groups (formed after the fact): group A, 6 athletes whose cortisol rose from baseline; group B, 6 with a decrease or no change. The abstract does not say which sample the split was made on; it follows the sentence on the 2nd test and gives the change from baseline.
Not given in the abstract: time of day and fasting state, fuelling and hydration during the run, assay methods, statistical tests, individual data, the size of the power changes, and perceived exertion (MEDLINE indexes the paper under Perception, which suggests it was recorded; inference).
Funding and interests: PubMed lists the publication type "Research Support, Non-U.S. Gov't"; Crossref names no funder; conflicts are not given in the abstract.

Key Results

Measure (abstract)Result
1st test (10 min at 70% VO2max, fresh)cortisol and GH up (P < 0.05); insulin down (P < 0.01); testosterone unchanged
2-h run (blood lactate about 2 mmol/l)insulin down; GH up; cortisol and testosterone variable
2nd test (after the run)insulin down further (P < 0.05); testosterone, GH and cortisol variable
Cortisol rise from baseline, group A (6) vs group B (6)+304.0 (60.0) vs +3.1 (5.3) nmol/l; between groups P < 0.05
GH following the 2nd test, group A vs group B+14.7 (4.8) vs +6.0 (2.9) ng/ml; "substantially higher"; no P value in the abstract
1-min anaerobic power, after vs before the rungroup A higher, group B lower (P < 0.05); no values in the abstract
What the P values can carry: the between-group P < 0.05 for cortisol tests the variable that defined the groups, so it adds nothing to the split. The GH difference has no P value in the abstract. The P < 0.05 for power is attached to the before-after comparison; whether the two groups differed from each other is not stated.
A small oddity: group B, described as "a decrease or no change", averaged +3.1 (SD 5.3) nmol/l, so at least one of its members rose slightly (our arithmetic).
Numbers in the newsletter summary that are not in the abstract: cortisol +43% vs −19%, 1-min power +4.1% vs −5.0%, GH +124% vs +71%. The −19% cannot describe the same change as the abstract's +3.1 nmol/l for group B.Read against the abstract's increments, +43% and +124% would imply starting values of about 707 nmol/l cortisol and 11.9 ng/ml GH (our arithmetic), a GH level that fits a concentration already raised by earlier exercise (the 1st test or the run) rather than a rested baseline (inference).The percentages may come from the paper's tables at another sampling point; this cannot be checked without the full text.

Mechanisms

Measured: fresh, a 10-min effort at 70% VO2max raised cortisol and GH and lowered insulin. After 2 h of running the same effort lowered insulin again, while the cortisol, GH and testosterone responses scattered between athletes; the half whose cortisol rose also had the larger GH rise and a higher 1-min power than before the run.
Authors' interpretation: the fatigue of prolonged endurance exercise may reset the pituitary-adrenocortical part of the endocrine system, showing either as intensified or as suppressed endocrine function.
Inference: the study does not show that the hormones changed the power. Both may reflect a third thing, such as how fatigued or how fuelled each athlete arrived; the abstract reports no training load, glucose or fuelling data with which to tell.
Inference: a suppressed hormonal response to a second bout is the pattern the overtraining consensus describes as a research marker of non-functional overreaching or overtraining (NFOR/OTS) in its two-bout maximal protocol (REF-206); group B could have been the more fatigued half going in. That was not measured here.
Inference: with no control session, a higher 1-min power after 2 h of moderate running could reflect warm-up or learning on a second all-out attempt as much as hormones. With a rest control, about an hour of moderate cycling lowered 30-s sprint power in REF-423.

Practical Application

Do bigger cortisol and growth-hormone rises mean better durability? Not shown. In 12 athletes split 6/6 after the fact, 1-min power rose after a 2-h run in the 6 whose cortisol rose, fell in the rest. One small study, 2001, abstract.
Nothing to test or train from this: no hormone measure, cut-off or intervention follows, and a blood cortisol or GH value is not a durability score (inference). The levers in the base remain fuelling (trial evidence), heavy strength (two small trials) and hard work late in long sessions (house practice) (SYNTH-32).
What it does show (B-, 12 athletes): the hormonal answer to a standard 10-min effort changes after 2 h of moderate running and differs widely between athletes; insulin fell further as a group, while cortisol rose in half the athletes and not in the other half.
A blunted second-bout response belongs to overreaching research, not to the field: the ECSS/ACSM consensus describes a two-bout protocol in which a blunted hormonal response to the second of two maximal bouts marks non-functional overreaching or overtraining (NFOR/OTS) as a research approach, and says no marker meets the criteria for routine use (REF-206).An athlete who is flat and fading across weeks needs the fuelling and overreaching checks, not a hormone reading (SYNTH-32: check fuelling before concluding the athlete is un-durable; the base's own practice).
A better sprint after a long easy run is not durability (inference): half these athletes had more 1-min power after 2 h of moderate running, half less.Short-effort power after long work varies in the base too: it fell after an hour of moderate cycling against a rest control (REF-423) and after 4 h of race-like riding (REF-144), while about 2000 kJ of easy riding did not significantly lower 3-min power in professionals (REF-193).Durability is read on the athlete's own fresh and fatigued efforts, CP or first threshold after hours of work (REF-1238, SYNTH-32).

Limitations

Abstract only. The paper is closed on the publisher's site (Springer, no access), has no PubMed Central copy and no repository copy in OpenAlex; descriptive data, the size of the power changes, sampling times, fuelling and statistics are not given in the abstract.
Groups formed after the fact on the variable compared. The 6 vs 6 split by cortisol response makes the cortisol difference circular; the GH and power differences are associations between two groups of 6, with no correlation across all 12 reported in the abstract and no way to tell which came first.
No control condition. Without the same tests on a day without the run, the before-after changes in power and hormones cannot be separated from warm-up, familiarisation or time of day (inference).
Markers, and one short effort. The main outcomes are blood hormone concentrations; the one performance outcome is a single 1-min anaerobic test of unstated mode, done once before and once after the run, with no values in the abstract.
Who and when. Twelve endurance-trained men (by MEDLINE indexing), 2001 assays, one 2-h run at moderate intensity; no women, no race-like or fuelled protocol.
Where a newsletter summary (October 2026) goes beyond the paper: (1) it calls the outcome "durability", but the abstract, title and keywords do not use the term and the study does not measure deterioration over hours of exercise; it compares one 1-min anaerobic test before and after a 2-h moderate run, and in the "better" group power rose rather than held; (2) it reports that the athletes were divided by cortisol response "for data analysis" but treats the group differences as findings, without saying that grouping on the cortisol response makes the cortisol difference circular and leaves the rest a 6 vs 6 association; (3) its headline, "greater increases in cortisol and growth hormone during exercise are associated with better durability", rests on 6 vs 6 athletes with no correlation and no causal test, and the authors' conclusion concerns an endocrine resetting by fatigue and makes no performance claim; (4) it says the study was published in 2021, while the paper and its own reference say 2001; (5) its percentages are not in the abstract, the −19% for the decreased-or-unchanged group conflicts with the abstract's +3.1 nmol/l, it calls the GH difference significantly greater where the abstract gives no P value, and it calls the 1-min power difference between the groups significant where the abstract attaches P < 0.05 to the before-after change; (6) it describes blood sampled before and after the run and leaves out the two 10-min tests at 70% VO2max around which the hormones were measured; (7) the cycling mode of the 1-min test is not in the abstract.The participants, the 2-h run at about 2 mmol/l, the 1-min test before and after, the 6 vs 6 cortisol split (though not its "before to after the 2-h run" definition, which the abstract does not give) and the direction of the power and GH differences match the abstract.
Funding: non-US-government research support per PubMed; the funder and any conflicts are not given in the abstract.
How this entry was checked and changed
Why this level

from the abstract; n = 12, uncontrolled pre-post, which is B by design; lowered for limitations beyond the design: the two groups of 6 were formed from the variable they are then compared on, the main outcomes are hormone concentrations (markers), and the one performance outcome, a 1-min anaerobic test, has no mode, timing or size of change in the abstract; fuelling, sampling times and statistics are not given