The time of day determines a muscle’s energy efficiency and metabolic response

Northwestern Medicine scientists have discovered circadian clocks in muscle tissue that control the muscle’s metabolic response and energy efficiency depending on the time of day.

The finding in mice, published in Cell Metabolism, sheds light on the time-of-day differences in muscle’s ability to adapt to exercise and use oxygen for energy. Muscle cells are more efficient during an organism’s normal waking hours, the study found.

All cells in the body, including those in muscle, contain a clock that regulates how cells adapt to changes in the environment and activity across the 24-hour day.

“Oxygen and the internal clock are doing a dance together inside muscle cells to produce energy, and the time of day determines how well that dance is synchronized,”  said senior author Joseph Bass, MD, PhD, chief and Charles F. Kettering Professor of Endocrinology in the Department of Medicine. “The capacity for a cell to perform its most important functions, to contract, will vary according to the time of day.”