REF-1535 · Ghiarone et al., 2019 · Journal of Applied Physiology · Paper · PubMed

Does a 2-h gap beat an overnight one with glycogen low both times?

In 15 active men over 3 wk, mitochondrial content showed no clear change in either arm; state 4 respiration and RPE favoured 2 h. No performance trial in the abstract.

Main caveat: Read from the abstract. No values, no glycogen data, no diet details from this paper; protocol details come from the later report, very likely on the same men.
limited, mixed evidenceMeasured on recreational people

Fifteen healthy men trained for 3 weeks on a long ride followed by interval work, with the two sessions either 2 h apart (twice-a-day, n = 8) or 14 h apart (once-daily, n = 7). The interval session started low on glycogen in both arms, so the fuel was meant to be equal and the gap was what differed.

Mitochondrial content and the measured proteins did not clearly move in either arm. Peak VO2 rose and lactate, oxygen cost and RPE during a 100-min task fell in both. Two results separated the arms in favour of the 2-h gap: state 4 respiration, which the authors call mitochondrial efficiency, and a larger fall in RPE.

Our reading: closing the gap to 2 h did not show up as more mitochondria in 3 weeks in these men, and it is one of the few direct tests of the gap with the fuel held low in both.

Protocol

What it isolates: the gap, with low glycogen before the second session in both arms. It does not isolate the gap fully: on the later report's description, the arms also differ in rest days (below) and in when the long ride falls. It has no single-session arm, so it cannot say whether two sessions beat one.
From this abstract: 100-min endurance exercise followed by high-intensity interval exercise 2 h (twice-a-day) or 14 h (once-daily) later, 3 weeks.
From the open full text of the later report, very likely on the same men ([REF-1547]), not from this paper: twice-a-day trained 3 days a week, ride from 07:00 to 09:00, intervals at 11:00. Once-daily trained 6 days a week, ride at 20:00, intervals at 11:00 the next day; that report gives this gap as 15 h, the abstract here as 14 h.
Sessions, same source: ride of 100 min at 50% of the difference between the first and second lactate thresholds, then after 8 min six 1-min bouts at 125% of peak power with 1 min rest. Intervals: 5-min warm-up, then ten 2-min bouts at 20% of the difference between second threshold and peak power, 1 min passive rest. Prescribed diet, not detailed there.
Measures, from the abstract: state 4 respiration, citrate synthase activity, mitochondrial and lipid area in two muscle regions, PGC-1α, PPARα and electron-transport protein, peak VO2, and plasma lactate, oxygen cost and RPE during a 100-min task.
Funding and interests: Crossref lists CAPES, CNPq and FACEPE. Conflicts not readable in the abstract record.

Key Results

MeasureOnce-daily (14 h, n = 7)Twice-a-day (2 h, n = 8)Between arms
State 4 respirationno clear improvementimprovedgroup × training P < 0.05
Citrate synthase activityno clear changeno clear changeP > 0.05
Mitochondrial and lipid area, both regionsno clear changeno clear changeP > 0.05
PGC-1α, PPARα, electron-transport proteinno clear changeno clear changeP > 0.05
Peak VO2roseroseno group effect reported in the abstract
Lactate and O2 cost, 100-min taskfellfellno group effect reported in the abstract
RPE, 100-min taskfellfell moregroup × time × training P < 0.05
No values in the abstract. Only directions and P thresholds are printed, so the size of the respiration and RPE differences cannot be stated here.
No clear difference, not "the same". The authors write that both approaches gave similar adaptations; no equivalence test is reported, and 7 or 8 men per arm could miss a real effect.
Very likely the same men, in the later report: graded-test duration rose from 41.6 ± 4.4 to 47.5 ± 4.9 min (once-daily) and from 42.4 ± 7.6 to 49.5 ± 8.7 min (twice-a-day), group × time P = 0.189, with one man dropped as a lactate outlier. Not an independent result.

Mechanisms

Measured: a change in state 4 respiration without a measured change in citrate synthase, mitochondrial area or the named proteins.
Authors' interpretation: the adaptations were broadly alike, with mitochondrial efficiency and perceived effort favouring the 2-h gap.
Inference: a respiration change with no change in content is a dissociation in one small trial, not a route to performance. The null on content in both arms could also mean that 3 weeks or this sample was too short or too small to show one.
Not measured, or not in the abstract: a time trial or race; threshold power; glycogen values; training quality in the second session; sleep; women.

Practical Application

Does a 2-h gap beat an overnight one with glycogen low both times? In 15 active men over 3 wk, mitochondrial content showed no clear change in either arm; state 4 respiration and RPE favoured 2 h. No performance trial in the abstract.
Good for: answering "does a shorter gap build more mitochondria?" with one direct test: not visibly, in 3 weeks, in these men.
Good for: keeping signal and adaptation apart. Read with REF-1536, the same project, where the 2-h gap gave stronger gene signals after one session.
Not good for: deciding one session against two. Both arms did both sessions.
Not good for: threshold doubles, trained athletes or women. None was tested here.
Not from this paper: what the base says about double threshold days is in SYNTH-03, and about fuelling a same-day double in SYNTH-85.

Limitations

Read from the abstract. No values, no glycogen data, no diet details from this paper; protocol details come from the later report, very likely on the same men.
Small and short: 15 men, 3 weeks.
The gap is not the only difference. On the later report's account, 3 training days a week against 6, and a morning against an evening long ride.
Gap reported two ways: 14 h here, 15 h in the later report; that report's clock times give about 13 h from end of ride to start of intervals (our arithmetic).
Not independent of [REF-1547], and from the same project as REF-1536.
Men only; no women, no competitive athletes.
How this entry was checked and changed
Why this level

(from the abstract) — parallel trial with 15 (rubric B: <20), one step lower: the results that separate the groups are a respiration marker and RPE, no performance trial appears in the abstract, and no effect sizes are printed there. Subscription article; no copy in PubMed Central or Europe PMC