ReviewCircadian aspects of body temperature regulation in exercise
Section snippets
Background
In this review, our main aims are to demonstrate the impact of circadian rhythms on thermoregulation and establish some consequences for physiological responses to exercise. A further aim is to place the role of ergogenic practices that manipulate body temperature in context of the circadian milieu. Finally, we consider how such fluctuations differ between males and females, individuals’ fitness and acclimatisation status, and exercise dimensions.
Circadian rhythms—general principles
The daily variations observed in circadian rhythms include endogenous (due to the “body clock”) and exogenous components. The exogenous influences consist of alterations in activity in accordance with the sleep-wake cycle, and changes in ambient temperature, as described above. The relative size of the endogenous and exogenous components of a circadian rhythm can be estimated by the “constant routine” protocol and “purification” methods. In the constant routine protocol, subjects remain awake
Exercise performance
Maximal exercise of short duration demonstrates circadian rhythmicity closely in phase and shape to that of core temperature. This similarity applies to isometric force (Coldwells et al., 1991), anaerobic power and anaerobic capacity (Reilly and Down, 1986, Reilly and Down, 1992), peak isokinetic torque, grip strength, joint flexibility and many other measures (Reilly, 1990). The rhythms are observable in simulations of competition and time-trials in cycle ergometry (Reilly and Baxter, 1983),
Interactions between the response to exercise and thermoregulation
Because similar thermoregulatory mechanisms are involved in the control of the circadian rhythm of resting core temperature and in reducing the temperature rise during exercise, interactions between them might exist (Fig. 2), particularly as the body clock and the thermoregulatory centres are in anatomical proximity within the hypothalamus (Reilly et al., 1997). Evidence supporting these predictions will now be considered.
Individual differences
There are individual differences in thermoregulatory responses to exercise. Among the factors involved are effects of gender, age and behavioural type. Responses also vary with training, acclimatisation and seasonal variations. These effects may have practical consequences for exercise and for circadian characteristics.
Overview
Models of thermoregulation must take into account the influences of circadian rhythms, independent of environmental factors. It seems that the set-point at rest is altered in a circadian fashion, reflecting the cyclic changes between the need for rest and for activity. As a result, the body temperature has been used as a marker of endogenous circadian rhythms and to track adaptations to disruptions such as occur in nocturnal shift work or travelling across multiple time zones. The circadian
References (98)
- et al.
The impact of altered climatic condititions and altitude on circadian physiology
Physiol. Behav.
(2007) - et al.
Exogenous melatonin enhances luteinizing hormone levels of women in the follicular but not in the luteal menstrual phase
Fertil. Steril.
(1995) - et al.
The prevention and treatment of jet lag
Sleep. Med. Rev.
(1999) The affects of gender, acclimation state, the opportunity to adjust clothing and physical disability on requirements for thermal comfort
Energy Build.
(2002)- et al.
Jet lag and air travel: implications for performance
Clin. Sports Med.
(2005) - et al.
Physiological effects of light on the human circadian pacemaker
Semin. Perinatol.
(2000) - et al.
Circadian and age-related modulation of thermoreception and thermoregulation: mechanisms and functional implications
Age. Res. Rev.
(2002) - et al.
Light of domestic intensity produces phase shifts of the circadian oscillator in humans
Neurosci. Lett.
(1998) - et al.
Jet lag: trends and coping strategies
Lancet
(2007) - et al.
Energy balance, metabolism, hydration and performance during strenuous hill walking: the effect of age
J. Appl. Physiol.
(2002)