The Study
Time-of-day effect of high-intensity muscle contraction on mTOR signaling and protein synthesis in mice
This study looked at how mouse muscles react to exercise at different times of day, and found that some tiny molecular signals change depending on whether it's daytime or nighttime. But it didn't measure if the muscles actually got bigger — so we can't say when's the best time to work out.
Analysis score
Maximum 72 for a cohort study.
Where the score came from
Scientists tested if mice grow bigger muscles when they exercise during sleep vs. when they're awake. They made their muscles contract with electric pulses at different times of day.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 519 / 100
Quality score
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Even though the body's internal clock affects baseline muscle activity, the muscle's immediate response to exercise doesn't change with time of day — so timing your workout may not matter for muscle growth.
- 2Muscle signaling molecules were more active during sleep, but the actual amount of new muscle protein made after exercise was the same no matter the time.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Scientific Reports
Year
2025
Authors
Taiga Mishima, Yosuke Takenaka, Akiko Hashimoto‐Hachiya, Y. Tanigawa, Natsumi Suzuki, Katsutaka Oishi, R. Ogasawara
Related Content
Claims (6)
When muscles contract under tension, the mTOR pathway is activated, leading to greater production of muscle proteins and an increase in muscle size.
In adult male C57BL/6J mice, muscle protein synthesis is naturally higher during the day than at night, but the surge in synthesis after intense muscle activity remains the same regardless of the time of day.
In adult male C57BL/6J mice, high-intensity muscle contraction leads to higher activation of mTORC1 signaling proteins during the light phase than during the dark phase, but the rate of muscle protein synthesis remains unchanged between these times.
In adult male C57BL/6J mice, REDD1 protein levels rise during the night and decrease when muscles contract, and these daily changes in REDD1 correspond to changes in how sensitive mTORC1 signaling is at different times of day.
In male C57BL/6J mice, corticosterone levels in the blood are highest during the day and coincide with increased REDD1 protein levels in muscle tissue, suggesting a link between daily hormone cycles and changes in how muscle responds to growth signals.
In adult male C57BL/6J mice, muscle contraction during the light phase increases phosphorylation of PRAS40, a protein that regulates mTORC1, and this change is linked to daily fluctuations in mTORC1 activity driven by Akt signaling.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.