Human circadian rhythms and exercise: Significance and application in real-life situations

Abstract

This review introduces a variety of human circadian rhythms including physiological processes and mental and physical performances, with reference to real-life situations. Circadian rhythms play a role in physiological processes, such as core body temperature and plasma mela-tonin, which are recognized as the body clock. As humans are diurnal organisms, mental per-formance declines primarily at night, secondarily in the early afternoon; this is consistent with risks of traffic and industrial accidents. Physical performance is composed of various fitness components and generally reaches its peak and nadir at around evening and early morning, re-spectively. Exceptions to this are body balance control and accuracy, both of which require brain function. Although maximal oxygen consumption (V ・ O 2 max) measured in the laboratory shows a constant value independent of the time of day, actual endurance capacity might be determined by core body temperature at the beginning of exercise, thermoregulatory response, and environ-mental temperature and humidity, all of which vary with the time of day. As the most powerful factor affecting the human circadian clock is bright light, physical exercise may be one factor entraining the human circadian pacemaker. However, experimental evidence has suggested that exercise itself has little or no influence on shifting the human master clock. Although further studies are required, recent studies have demonstrated that physical exercise at a certain time of day specifically improves physical performance at the same time, which might be independent of the master clock.