REF-1551 · Hearris et al., 2019 · Journal of Applied Physiology · Paper · PubMed

Does going lower on glycogen buy more signal?

In 8 men starting at 88, 185 or 278 mmol/kg dw, capacity was 18, 36 and 44 min, with AMPK and PGC-1α reported comparable. One session, sleep-low model, not a same-day double.

Main caveat: Read from the abstract. Training status, order of conditions, and depletion details are missing.
limited, mixed evidenceMeasured on a mixed group

In repeated measures, eight men did an evening session to deplete glycogen, then took 0, 3.6 or 7.6 g/kg of carbohydrate over the next 6 h before sleeping. The next morning they did 8 × 3 min at 80% of peak power, then 1-min efforts until exhaustion. Starting glycogen was graded (88 ± 43, 185 ± 62, 278 ± 47 mmol/kg dw) and capacity differed (18 ± 7, 36 ± 3, 44 ± 9 min).

AMPK phosphorylation and PGC-1α mRNA rose by similar amounts across conditions. p38, CaMKII and the mRNA of p53, Tfam, CPT-1, CD36 and PDK4 showed no clear effect of exercise or carbohydrate. The authors conclude that when glycogen is under 300, further drops of 100 mmol/kg dw cost capacity without adding signal.

Our reading: a test from below of the glycogen threshold idea in REF-543, with the cost in work clearly shown and the signal read at different amounts of work.

Protocol

What it isolates: the fuel at the start of a session, below 300 mmol/kg dw, with the same depletion and overnight gap. It does not test two sessions in a day, the gap or the order.
Who: 8 men; training status not given in the abstract.
Depletion: evening cycling protocol, details not given in the abstract.
Fuel: 0 (L-CHO), 3.6 (M-CHO) or 7.6 g/kg (H-CHO) of carbohydrate over 6 h before sleep.
Test: next morning, 8 × 3 min at 80% of peak power output, then 1-min efforts at 80% until exhaustion.
Measures: muscle glycogen; AMPK, p38 and CaMKII phosphorylation; PGC-1α, p53, Tfam, CPT-1, CD36 and PDK4 mRNA, after exercise and 3 h after.
Funding and interests: not readable in the abstract record.

Key Results

MeasureL-CHO (0 g/kg)M-CHO (3.6 g/kg)H-CHO (7.6 g/kg)Between conditions
Muscle glycogen before exercise (mmol/kg dw)88 ± 43185 ± 62278 ± 47P < 0.05
Capacity at 80% of peak power (min)18 ± 736 ± 344 ± 9P < 0.05
AMPK phosphorylation after exerciseabout 4-foldabout 4-foldabout 4-foldreported comparable
PGC-1α mRNA 3 h after exerciseabout 5-foldabout 5-foldabout 5-foldreported comparable
p38, CaMKII; p53, Tfam, CPT-1, CD36, PDK4 mRNAno clear effectno clear effectno clear effectno clear effect
The authors' figure: each graded drop of 100 mmol/kg dw cut capacity by 20-50%. Our arithmetic: 44 to 36 min is 18% lower, 36 to 18 min is 50% lower, and 18 against 44 min is 59% lower.
Our arithmetic: the 8 × 3 min block alone is 24 min at 80% of peak power, so a mean of 18 min in L-CHO suggests that, on average, these men did not finish the prescribed block (inference).
Comparable, not "the same": no equivalence test appears in the abstract, and n = 8.

Mechanisms

Measured: a dose response of capacity to glycogen, with the kinases and genes above.
Authors' interpretation: below 300 mmol/kg dw, lower glycogen does not add to the signalling, and costs capacity. They draw this as an implication for carbohydrate periodisation.
Inference: a comparable signal arose from about 18 min of work in one condition and about 44 min in another. So "no added signal" is true of the total reading, and it does not settle signal per unit of work. A matched-work comparison was not done here.
Not measured, or not in the abstract: adaptation over weeks, performance after a training block, same-day sessions, sleep quality after the evening depletion, women.

Practical Application

Does going lower on glycogen buy more signal? In 8 men starting at 88, 185 or 278 mmol/kg dw, capacity was 18, 36 and 44 min, with AMPK and PGC-1α reported comparable. One session, sleep-low model, not a same-day double.
Good for: the cost side of very low glycogen: much less work done at a set intensity.
Good for: doubt about "the lower the better" in train-low, at least below 300 mmol/kg dw.
Not good for: claiming low glycogen is pointless. The range tested sits under 300; it does not test high against low (REF-1537 pools that).
Not good for: a same-day double. Nothing here varied or included a second session on the same day.
Not from this paper: the base's fuelling practice around key sessions is in SYNTH-69 and for a close next session in SYNTH-85.

Limitations

Read from the abstract. Training status, order of conditions, and depletion details are missing.
n = 8, men only.
Unequal work before the signal was read, so the signal comparison is not at matched work (inference).
Wide glycogen spread within arms (SD 43-62 mmol/kg dw), and steps of about 100 mmol/kg dw.
The range is under 300 mmol/kg dw, so it does not test a well-fed comparison.
Single session, no adaptation or training outcome.
How this entry was checked and changed
Why this level

(from the abstract) — repeated measures with 8 (rubric B: crossover <15), one step lower: order is not stated, the headline outcome beside capacity is a marker, and the arms differ in the work done before the signal was read. Subscription article; no copy in PubMed Central or Europe PMC