The circadian typology: the role of physical activity and melatonin

Circadian rhythms influence our daily behavior. Individuals display preferences for activity at certain time of day and this circadian phenotype can be summarized with the concept of “chronotype” or circadian typology (CT). The chronotypes differ in the timing of many physiological and psychological variables. Individuals with an early circadian phase are morning-types (M-types), those with a delayed circadian phase are evening-types (E-types), and those with an intermediate circadian phase are neither-types (N-types). Nevertheless, the propensity toward morning or evening preferences can vary during the life. In particular, adolescence can represent a crucial time in which the sleep–wake cycle tends to become delayed. The circadian rhythm desynchronization is common in modern society and lead to negative health effects, not only for physical health, but also for cognitive and affective function. One of the most important variables that show a defined circadian rhythm is melatonin; human melatonin levels increase at night, but the acrophase of melatonin occurs earlier in M-type than in E-type. Aim of this review, after providing a description of the methods for detecting the CT, analyzes the propensity toward morning or evening preferences in different life periods and the interactions between melatonin and physiological functions associated to physical activity. Exercise, performed in morning or in evening sessions, can adjust circadian rhythm, supporting its application as a treatment for the circadian rhythm desynchronization, for example, resulting from jet lag or shift work. Interindividual differences should also be taken into account in case of changes of the circadian rhythms parameters of different variables that can influence health also in relation to sport.