REF-325 · Basti A, Yalcin M, Herms D, Hesse J, Aboumanify O, Li Y, Aretz Z, Garmshausen J, El-Athman R, Hastermann M, Blottner D & Relogio A, 2021 · BMJ Open Sport & Exercise Medicine, · Paper · PubMed

Diurnal variations in the expression of core-clock genes correlate with resting muscle properties and predict fluctuations in exercise performance across the day

In 21 healthy adults, exercise performance peaked in the late afternoon (15-18 h), resting muscle tone (MyotonPRO) varied across the day, and HIGHER tone went with BETTER performance; core-clock gene rhythms in hair, blood or saliva correlated with both

Blimited evidenceMeasured on recreational to trained athletesWritten before October 2026, being re-checked

Participants

n=21 healthy participants (13 men, 8 women) across three test series: 15 provided hair, blood or saliva time-course samples for core-clock gene expression (RT-PCR); 16 did strength and endurance exercise tests at 9 h, 12 h, 15 h and 18 h; myotonometry (MyotonPRO, five muscles) in 11

Protocol

Core-clock gene expression rhythmicity from peripheral samples
Strength and endurance exercises at four times of day (9, 12, 15, 18 h)
Resting muscle tone by MyotonPRO in five muscles
Computational analysis relating gene expression, resting muscle tone and exercise performance

Key Results

Core-clock genes showed daily fluctuations in expression in all sample types for all participants
Exercise performance peaked in the late afternoon (15-18 h) for both men and women, with variation depending on the type of exercise (strength vs endurance)
Muscle tone varied across the day, and HIGHER muscle tone correlated with BETTER performance
Molecular daily profiles correlated with the daily variation in exercise performance
Authors: training programmes could be timed from individual molecular data; relevant to elite sport and to rehabilitation

Mechanism

Resting muscle tone here is a physiological, time-of-day property that rose and fell with the clock and with performance — higher tone, better output. Inference, not tested: this is a different quantity from the post-exercise stiffness elevation measured in the damage studies (Kong 2018 REF-317, Wilke 2022 REF-318); the same instrument reads both, so a myotonometry reading has to be interpreted against time of day before it is read as "recovery".

Practical Application

In 21 healthy adults tested at 9, 12, 15 and 18 h, strength and endurance performance peaked at 15-18 h; resting muscle tone varied across the day and higher tone went with better performance — "more tone" was the ready state here, not the fatigued one
Inference, not tested: because performance peaked late afternoon, the morning reading of the same muscle would be expected to be lower in tone and performance; the abstract states the peak, not the morning values
Time of day is a confounder for any stiffness or tone tracking: compare readings taken at the same clock hour
Not from this paper; the base's own practice: put quality sessions (intervals, tests) in the late-afternoon window when the schedule allows; the study shows a group-level peak, with the type of exercise mattering, and did not test training at different times

Limitations

Small subset for muscle measurements (n=11); n=15-16 for the other series
Lab conditions — real-world training context not assessed
Correlational; no intervention on training time
How this entry was checked and changed
Why this level

regraded 2026-09-27 from B+: correlational study, n=21 (muscle tone in 11)

Content correction 2026-09-27
"Morning = lower tone = lower performance" -> the abstract states the late-afternoon peak (15-18 h) and the tone-performance correlation; the morning half is inference and is labelled so.
"Two types of muscle tone: physiological vs pathological" and the Bakken framing -> relabelled as inference/house; the study measured resting tone only, not post-exercise stiffness.
Level B+ -> B (correlational, n=21).