Diurnal variations in muscle and liver glycogen differ depending on the timing of exercise

Abstract

It has been suggested that glycogen functions not only in carbohydrate energy storage, but also as molecular sensors capable of activating lipolysis. This study aimed to compare the variation in liver and muscle glycogen during the day due to different timing of exercise. Nine healthy young men participated in two trials in which they performed a single bout of exercise at 70% of their individual maximal oxygen uptake for 60 min in the post-absorptive (morning) or post-prandial (afternoon) state. Liver and muscles glycogen levels were measured using carbon magnetic resonance spectroscopy (13C MRS). Diurnal variations in liver and muscle glycogen compared to baseline levels were significantly different depending on the timing of exercise. The effect of the timing of exercise on glycogen fluctuation is known to be related to a variety of metabolic signals, and the results of this study will be useful for future research on energy metabolism.

Daily running enhances molecular and physiological circadian rhythms in skeletal muscle

“…These data suggest that enhanced maximum speed at ZT21 in mice that experience daily moderate activity is associated with increased selective utilization of carbohydrates for energy production during exercise at ZT21. Consistent with this proposition, a recent study showed that humans exhibit a significantly increased respiratory exchange ratio (RER, a measure of the relative utilization of carbohydrates and fats for energy production) when performing exercise in the afternoon compared to the same exercise performed in the morning [ 27 ]. Similarly, the impact of exercise on lipids, carbohydrates, and other metabolites in several mouse organs depends on the time of day at which exercise is performed [ 28 ].…”

New Horizons in Carbohydrate Research and Application for Endurance Athletes

“…It is often overlooked that if competition is to be performed in the morning after an overnight fast (or any period of prolonged fasting), liver glycogen stores may be compromised. Namely, in the postabsorptive phase (e.g., during the night) liver glycogen stores decrease [ 41 ]; so, in the morning they can be substantially depleted [ 42 ]. On the contrary, muscle glycogen stores are typically not affected by an overnight fasting period [ 42 ].…”

“…Namely, in the postabsorptive phase (e.g., during the night) liver glycogen stores decrease [ 41 ]; so, in the morning they can be substantially depleted [ 42 ]. On the contrary, muscle glycogen stores are typically not affected by an overnight fasting period [ 42 ]. As numerous competitions start in the morning, it is pertinent that the meals after overnight fast are designed so that there is a focus on liver glycogen repletion.…”

Editorial for “Short‐Term Variability of Proton Density Fat Fraction in Pancreas and Liver Assessed by Multi‐Echo Chemical‐Shift Encoding‐Based MRI at 3 T”

“…For instance, a previous study showed that extreme changes in liver glycogen concentration affect liver T 1 measurements 1 . Given the natural diurnal variation of liver glycogen concentration, 2 these T 1 variations will likely be lower and within the single‐session reproducibility range reported for liver T 1 3 in healthy volunteers and most patients. However, this effect could be exacerbated by impaired glucose metabolism in patients who have T2DM 4 .…”