Hormonal
The reduced force production in the morning is mechanistically linked to lower calcium availability for contractile units, as indicated by reduced caffeine-induced contracture force.
This is a basic science finding. It suggests that the reason morning muscles might be weaker is not just neural, but involves how much calcium is available to trigger contraction. This is not directly actionable for training but informs future research on timing.
Caffeine-induced contracture force... was reduced in Morning-SC þ mice compared with SC- counterparts... suggesting lower tetanic/eccentric forces in Morning-SC þ animals may be due to a reduced volume of Ca ++ available to contractile units.
Why this rating
The study uses caffeine contracture as a valid surrogate for calcium availability, but it is an indirect measure and does not directly quantify intracellular calcium kinetics.
Source
Time-of-day effects on ex vivo muscle contractility following short-term satellite cell ablation
Ryan E. Kahn et al. · American Journal of Physiology-Cell Physiology · 2024
DOI 10.1152/ajpcell.00157.2024
More from this paper
- The presence of satellite cells reduces ex vivo skeletal muscle force production specifically during the morning, whereas this effect is absent in the afternoon.Moderate
- The reduced force production in the morning associated with satellite cells results in significantly less contractile injury (force loss and dystrophin-negative fibers) following eccentric exercise.Moderate
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