Human muscles work to a biological clock, new research has discovered.
The body is known to be in sync with an invisible ticker, which controls the release of hormones, the digestive system and other crucial processes that keep us going throughout the day and night.
Now scientists from the University of Bath, the Universite Claude Bernard in Lyon, Ecole Polytechnique Federale de Lausanne (EPFL), the University of Surrey and the Nestle Institute of Health Sciences have found that this clock also affects muscles.
It was found that levels of different types of fat (lipids) in our muscle cells can vary throughout the day, with different kinds chosen at different times.
To come to their conclusions, the team tested volunteers, synchronising each subject's master clock by setting them all the same daily eating and sleeping routine a week leading up to the experiment. Researchers would analyse lipid composition in small samples from the thigh muscle tissue every four hours.
These showed a correlation between the muscle's lipid composition and the hour of the day, with co-author Professor Howard Riezman from the Biochemistry Department of the Faculty of Sciences at the University of Geneva saying, "As the combination of lipids varied substantially from one individual to another, we needed further evidence to corroborate these findings."
A second stage of the test involved an in-vitro experiment, in a controlled environment. Human muscle cells were grown and artificially synchronised using a signal molecule normally found in the body to resemble a biological clock. The lipid composition showed the same results, but when the experts disrupted the clock by inhibiting the genes, most of the periodically changing variations in the lipids were lost.
Ursula Loizides-Mangold, also from the University of Geneva, predicts the muscle's biological clock could help control the cells' sensitivity to insulin, thus affecting the muscle's ability to take in blood sugar - a key aspect in tackling conditions like diabetes.
"We have clearly shown that this variation of lipid types in our muscles is due to our circadian rhythm," Loizides-Mangold, explained. "But the main question is still to be answered: what is this mechanism for?"