Edinburgh Napier University, United Kingdom
Received Date: July 15, 2015; Accepted Date: August 08, 2015; Published Date: August 19, 2015
Citation: Boukelia B (2015) Exercise, Immune System and Circadian Rhythm. J Sports Med Doping Stud 5:163. doi:10.4172/2161-0673.1000163
Copyright: © 2015 Boukelia B. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Abnormal circadian rhythms have been linked to illnesses such as diabetes, depression , bipolar disorder , seasonal affective disorder (SAD)  and even obesity . Furthermore, circadian rhythms can affect body function and health due to sleep-wake cycles, body temperature , hormone release , and other important body functions. More recent studies have investigated other performance parameters that have also been found to possess a circadian rhythmicity, such as, stroke volume, cardiac output, blood pressure, vascular blood flow, metabolic rate, sweat rate and trunk flexibility .
The link between circadian rhythmicity and sport performance has been extensively studied with several contributing factors having been identified. These factors can be endogenous, including physiological changes such as core body temperature; and exogenous, including environmental changes such as sleep deprivation, and daily training time . Identifying the cause for improved performance is often difficult because performance fluctuations can be affected by different exogenous and endogenous factors occurring at the same time of day.
The indirect evidence for the existence of circadian rhythmicity in sports performance can be examined by the time of day athletes perform best or worst in actual sporting events . However, a great many sporting events are scheduled for the evening which may create a false circadian record. It is important therefore for coaches and athletes to be aware of how the time of day affects various and inter-related components of sport performance.
The circadian rhythm of the immune system and sport performance is still a new field of research, although it has been reported that circadian rhythmicity exists in the human immune system for some time [9,10]. Kimura et al. found that the circulation of the white blood cells involved in the defence of the human body show high-amplitude circadian rhythmicity: being lower in the morning and higher in the afternoon .
The immune system plays an important role in human health and the prevention of illness. In a review conducted by Gleeson et al. moderate exercise reduces the risk of chronic metabolic and cardiorespiratory diseases , in part because exercise exerts antiinflammatory effects which is mediated through the reduction in visceral fat mass (adipokines decrease) and the induction of an antiinflammatory environment with each bout of exercise. However, preventing athletes from illness during heavy training periods and/or races is a high priority for athletes, coaches and exercise researchers. A perception exists that some athletes, especially those engaging in prolonged intensive exercise and competition, such as running, cycling and swimming, may show an increased rate of upper respiratory tract infection (URTI) during intense training periods and competition . Given the considerable economic and personal investment in preparing athletes for events, there is a need to identify strategies to improve host resistance whilst minimising the risk of illnesses that may affect athletic performance. An agreement between scientists exists in that moderate exercise enhances the athlete’s immunity, but high-intensity prolonged exercise impairs, temporarily, immune competence. In addition, a relationship between immune-depression and risk of URTI has been established following heavy exercise .
The inverse relationship between exercise workloads and immune system function has been studied intensively . A number of studies have reported that exercise leads to a considerable physiological change in the human immune system . However, immune suppression is higher in some athletes compared to general active population , while there does appear to be a secondary response in truly elite athletes which reverses this theory. Although modest exercise may enhance the function of the immune system above sedentary levels; prolonged high-intensity exercise can weaken the immune competence of trained athletes. It may be that this relationship is most likely affected by individual determinants such as circadian rhythmicity, dietary status, allergies or environmental conditions. An important finding of Boukelia et al., is that exercise in hot and humid conditions can allow for changes to the intensity of airway inflammation and is more effective in the evening were phase response for and recovery period of CC16 and white blood cells are high in the evening . This finding may improve the treatment strategy in athletes suffering from upper airway dysfunction and could even be applied within an unhealthy population with a chronic disease such as asthma. This can be due to adaptive response rather than airway damage.
Athletes, coaches and event organisers can program their race events or training to target the time when athletes perform best and should consider the immunological and physiological parameters that can enhance performance.
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