Intrinsic Skeletal Muscle Function and Contraction-Stimulated Glucose Uptake Do Not Vary by Time-of-Day in Mice

Area of Science:

• Physiology
• Chronobiology
• Metabolism

Background:

• Skeletal muscle function and glucose metabolism exhibit daily variations.
• Chronobiological effects on intrinsic muscle properties are hypothesized as the cause.
• Direct investigation of these effects over a 24-hour cycle is lacking.

Purpose of the Study:

• To investigate time-of-day effects on intrinsic skeletal muscle contractile function and glucose metabolism.
• To determine if circadian variations influence exercise performance and glucose uptake in mouse skeletal muscle.

Main Methods:

• Assessed intrinsic contractile function, endurance, and contraction-stimulated glucose uptake.
• Utilized isolated extensor digitorum longus and soleus muscles from mice.
• Measurements were taken at four distinct times of day (zeitgeber times 1, 7, 13, 19).

Main Results:

• Circadian-related gene expression changes were observed in both muscles.
• No significant differences were found in contractile function, endurance, or glucose uptake across the four time points.
• These findings were consistent regardless of sex.

Conclusions:

• Time-of-day variations in exercise performance are not attributable to intrinsic muscle function.
• The glucose-lowering benefits of exercise are not mediated by chronobiological effects on muscle.
• Intrinsic skeletal muscle properties do not appear to be the primary driver of daily performance or metabolic responses to exercise.