When should I run—the role of exercise timing in metabolic health

Abstract The prevalence of type 2 diabetes is reaching epidemic proportions. First line therapy approaches are lifestyle interventions including exercise. Although a vast amount of studies reports on beneficial effects of exercise on metabolism in humans per se, overall data are contradictory which makes it difficult to optimize interventions. Innovative exercise strategies and its underlying mechanism are needed to elucidate in order to close this therapeutic gap. The skeletal muscle produces and secretes myokines and microRNAs in response to exercise and both are discussed as mechanisms linking exercise and metabolic adaptation. Aspects of chronophysiology such as diurnal variation in insulin sensitivity or exercise as a signal to reset dysregulated peripheral clocks are of growing interest in the context of impaired metabolism. Deep insight of how exercise timing determines metabolic adaptations is required to optimize exercise interventions. This review aims to summarize the current state of research on the interaction between timing of exercise and metabolism in humans, providing insights into proposed mechanistic concepts focusing on myokines and microRNAs. First evidence points to an impact of timing of exercise on health outcome, although data are inconclusive. Underlying mechanisms remain elusive. It is currently unknown if the timed release of mykokines depends on time of day when exercise is performed. microRNAs have been found as an important mediator of processes associated with exercise adaptation. Further research is needed to evaluate their full relevance. In conclusion, it seems to be too early to provide concrete recommendations on timing of exercise to maximize beneficial effects.