Endocrine Abstracts

Regular exercise training has widespread health benefits by positively affecting nearly all organ systems of the body. Human physiology and the adaptive response to acute and chronic exercise training have largely been elucidated in the field of exercise science. This field has used model systems, organisms and has a strong history of human studies. Recently, the effect of exercising at different times of day and the interaction of exercise with circadian rhythm has been of growing interest in the field. Environmental cues, such as the Earth’s day-night rhythm, partly regulate diurnal endocrine signalling molecules and metabolites. Circadian physiology consists of highly conserved biological processes over ~24-h cycles, which are influenced by external cues (Zeitgebers – ‘time-keepers’). Skeletal muscle has diurnal variations of a large magnitude, owing in part to the strong nature of physical activity throughout the day and other external Zeitgebers. Exercise also interacts with circadian rhythm in a bi-directional manner. Skeletal muscle contractions can alter the rhythmic cycling of the molecular clock, and exercise capacity is altered at different times of the day. Modelling this in cell and mouse models has many challenges, although these models are essential to uncovering the chronobiology connected to exercise. From integrating these models, and human data, our evidence suggests these diurnal variations are disrupted in the skeletal muscle of people with Type 2 Diabetes and this disruption is linked to aberrant cross-talk between the molecular clock and mitochondria. Additionally, exercise is a potent therapeutic intervention in many metabolic diseases. However, exercise at different times of the day in people with Type 2 Diabetes may have opposing outcomes on glycaemia during the day of exercise. Optimising exercise timing, therefore, might be a valuable contributor to improving treatment regimens of people with metabolic and endocrine disorders.