Chrono-exercise: Time-of-day-dependent physiological responses to exercise

Abstract

Exercise is an effective strategy to prevent and improve obesity and related metabolic diseases. Exercise increases the metabolic demand in the body. Although many of the metabolic health benefits of exercise depend on skeletal muscle adaptations, exercise exerts many of its metabolic effects through the liver, adipose tissue, and pancreas. Therefore, exercise is the physiological state in which inter-organ signaling is most important. By contrast, circadian rhythms in mammals are associated with the regulation of several physiological and biological functions, including body temperature, sleep-wake cycle, physical activity, hormone secretion, and metabolism, which are controlled by clock genes. Glucose and lipid tolerance reportedly exhibit diurnal variations, being lower in the evening than in the morning. Therefore, the effects of exercise on substrate metabolism at different times of the day may differ. In this review, the importance of exercise timing considerations will be outlined, incorporating a chrono-exercise perspective.

Keywords: Chrono-exercise; Circadian rhythm; Energy metabolism; Exercise timing; Inter-organ communication.

Fig. 1

Schematic diagram of chrono-exercise. There are two aspects to chrono-exercise. The effect of exercise timing on a biological clock (A), Considering the diurnal variation of substrate metabolism, hormones, and other factors regulated by the biological rhythm, exercise timing is considered (B).

Fig. 2

The architecture of the circadian system The biological clock is divided into the central clock and the peripheral clock. The central clock resides in the suprachiasmatic nucleus (SCN) in the hypothalamus of the brain. Light is the most powerful stimulus that regulates the central clock, and this stimulus is transmitted through the optic nerve of the eye to the SCN, where the internal clock is synchronized. Signals from the central clock are transmitted to peripheral tissues by humoral and neural factors such as hormones to synchronize the peripheral clocks. On the other hand, exercise and food intake synchronize the body clock without mediating the central clock. Also, the synchronization of clocks in different tissues creates a coordinated circadian rhythm of metabolic processes such as insulin secretion, cholesterol synthesis, and energy expenditure.

Fig. 3

Organs and tissues affected by exercise Exercise has tremendous health benefits, including reducing the incidence and severity of metabolic diseases and increasing healthy life expectancy. In addition, peripheral organs and tissues engage in inter-organ crosstalk through bioactive substances such as hormones and cytokines.

Fig. 4

The effect of different exercise timings on metabolic health.