A growing body of data suggests that skeletal muscle contractile function and glucose metabolism vary by time-of-day, with chronobiological effects on intrinsic skeletal muscle properties being proposed as the underlying mediator. However, no studies have directly investigated intrinsic contractile function or glucose metabolism in skeletal muscle over a 24 h circadian cycle. To address this, we assessed intrinsic contractile function and endurance, as well as contraction-stimulated glucose uptake, in isolated extensor digitorum longus and soleus from female mice at four times-of-day (Zeitgeber Times 1, 7, 13, 19). Significantly, while both muscles demonstrated circadian-related changes in gene expression, intrinsic contractile function, endurance, and contraction-stimulated glucose uptake were not different between the four time points. Overall, these results demonstrate that time-of-day variation in exercise performance and the glycemia-reducing benefits of exercise are not due to chronobiological effects on intrinsic muscle function or contraction-stimulated glucose uptake.
Impact statement: Ex vivo testing demonstrates that there is no time-of-day variation in the intrinsic contractile properties of skeletal muscle (including no effect on force production or endurance) or contraction-stimulated glucose uptake.