Fatigue and Biological Rhythms
Giovanni Costa Università di Verona, Italy
This chapter is concerned with temporal factors affecting human performance and work efficiency. The aim is to emphasize that a careful consideration of the temporal structure of body functions and, consequently, a proper timing of work activities can be of paramount importance to ensure high levels of performance efficiency, decreasing fatigue and enhancing health and safety.
The temporal organization of the biological systems is one of the most remarkable characteristics of the living organisms. In the last few decades chronobiology has highlighted the importance of this aspect for the human life, revealing the complex mechanisms underlying the temporal interactions among the various components of the body (systems, organs, tissues, cells, subcerular structures).
These are characterized by a large spectrum of rhythms having different frequencies and amplitudes. According to their periodicity (τ), three main groups of biological rhythms have been defined: (a) ultradian rhythms (τ ≤ 20 hr), such as heart rate, respiration, and electric brain waves; (b) circadian rhythms (20 ≤ τ ≤ 28 hr), such as the sleep/wake cycle or temperature; (c) infradian rhythms (τ ≥ 28 hr), among which circaseptan (weekly), circatrigintan (monthly), and circannual rhythms can be found, like immunological response, the menstrual cycle, and seasonal mood/hormonal changes, respectively.
Circadian (Latin: circa diem = about a day) rhythms are the most extensively studied due to their great influence on everyday life.
The human is a daylight creature; in the course of evolutionary adaptation, the human species has associated its own state of wakefulness and activity (ergotropic phase) with the day/light period and its sleep and rest state (trophotropic phase) with the night/dark period.