REF-1536 · Andrade-Souza et al., 2020 · FASEB Journal · Paper · PubMed

Does a bout 2 h after the first signal more than one 15 h later, glycogen low both ways?

In men, PGC-1α and PPAR transcription were higher at 2 h. Markers around one session; no training, no performance.

Main caveat: Read from the abstract. Sample size, glycogen values and effect sizes are missing, so the size of the signal cannot be stated.
thin evidenceMeasured on recreational people

The authors asked whether the stronger signals reported after train-low come from low glycogen or simply from two sessions falling close together, since a first session is what lowers the glycogen. They varied the time between a depleting session and a second session, 2 h or 15 h, with the second session starting low on glycogen both ways.

The 2-h version went with more TFEB and NFAT in the nucleus and more transcription of PGC-1α, PPARα and PPARβ/δ than the 15-h version. Their conclusion is that part of the train-low signal may belong to the closeness of the sessions.

Our reading: this is a direct statement of the case for a stronger signal from a close second session, in markers only, and the three-week report from the same project did not show more mitochondria (REF-1535).

Protocol

What it isolates: the gap between two sessions, with glycogen low before the second both ways. Fuel is held, so far as the abstract says, and the comparison is two sessions close together against two sessions apart.
From this abstract: a first glycogen-depleting session, then a second session 2 h (twice-a-day) or 15 h (once-daily) later.
From the open full text of the later report ([REF-1547]), not from this paper: three trials in random order. Once-daily: 100-min ride plus six sprints at 20:00, overnight fast, low-carbohydrate breakfast at 08:00, intervals at 13:00. Twice-a-day: low-carbohydrate breakfast at 08:00, ride and sprints at 09:00, intervals at 13:00.Control: same breakfast, intervals at 13:00, no depletion. Biopsies before, just after and 3 h after the intervals; no food from breakfast until the last biopsy.
Control arm: the abstract here reports only the 2-h against 15-h comparison; what the control arm showed for these genes is not in it.
Funding and interests: Crossref lists CAPES and the Australian Research Council. Conflicts not readable in the abstract record.

Key Results

Measure2 h against 15 h, per the abstract
Nuclear TFEBhigher at 2 h
Nuclear NFAThigher at 2 h
PGC-1α transcriptionhigher at 2 h
PPARα transcriptionhigher at 2 h
PPARβ/δ transcriptionhigher at 2 h
No numbers. The abstract prints no n, fold change, p value or glycogen concentration.
Later report, 5 participants from the project's "first study" (very likely this one; not named there): MCT1 mRNA 3 h after the intervals about 80% higher at 2 h than at 15 h (P = 0.038; REF-1547). MCT4 showed no clear effect.
Our arithmetic on the clock times above: 13:00 is 4 h after a 09:00 start and 17 h after a 20:00 start; with about 2 h of riding and sprints, that fits the stated 2 h and 15 h, end of one session to start of the next.

Mechanisms

Measured: nuclear abundance of two transcription factors and transcription of three metabolic regulators.
Authors' interpretation: some of the signal credited to train-low may come from close proximity of sessions, and twice-a-day might be an effective route to mitochondrial biogenesis and fat oxidation. This is their suggestion; biogenesis was not measured.
Inference: at 2 h the response to the first session may still be running when the second begins (compare the elevated PGC-1α mRNA 3 h after a first session in REF-1548). So a higher reading may be two responses added together rather than one amplified. The abstract cannot separate these.
Not measured, or not in the abstract: enzymes, mitochondrial content, any performance, any repeat over days, women. No arm compared two sessions with one at matched total work.

Practical Application

Does a bout 2 h after the first signal more than one 15 h later, glycogen low both ways? In men, PGC-1α and PPAR transcription were higher at 2 h. Markers around one session; no training, no performance.
Good for: the reason people give for doubles, as one direct test, with its limit attached: a signal after one session, in non-athletes.
Good for: a warning about train-low signals. Some may reflect closeness of sessions rather than low fuel, so the two cannot be assumed apart in classic designs.
Not good for: claiming adaptation. Three weeks in the same project gave no clear gain in mitochondrial content in either arm (REF-1535).
Not good for: planning trained athletes' weeks. Trained cyclists on stacked sessions did not show a between-group performance gain (REF-1096, REF-1097); those trials also changed the fuel.

Limitations

Read from the abstract. Sample size, glycogen values and effect sizes are missing, so the size of the signal cannot be stated.
Markers only, around one exercise bout, with no training period.
Protocol known through a later report from the same project, not from this paper.
The arms differ in more than the gap (inference from the clock times): a night's sleep and an overnight fast fall between sessions only in the 15-h arm.
No single-session comparison at matched work, so nothing here compares a double with one session.
Not independent of [REF-1535] or [REF-1547]. Whether its men are also those of the 3-week trial is not stated.
Men only.
How this entry was checked and changed
Why this level

(from the abstract) — mechanistic laboratory study with no performance outcome (rubric C+); n, glycogen values and effect sizes are not in the abstract. Crossref lists a CC BY-NC licence, but there is no copy in PubMed Central or Europe PMC