A recent Heliyon review describes the importance of the circadian rhythm (CR) and the underlying mechanisms of CR in sports performance. The study findings also highlight the unique role of CR in immune system function and the reciprocal link between CR, endocrine homeostasis, and sex differences.
Study: Narrative review: The role of circadian rhythm on sports performance, hormonal regulation, immune system function, and injury prevention in athletes. Image Credit: Jacob Lund / Shutterstock.com
CRs are daily shifts in biological and behavioral activity due to an organism’s natural capacity to synchronize with the environment’s 24-hour cycle of light and darkness. CRs originate from the body’s biological clock that regulates many elements, such as the sleep cycle and body temperature.
The central circadian pacemaker in humans is the suprachiasmatic nucleus (SCN). The SCN coordinates various activities, including neuronal activation, hormone production, and temperature fluctuations following solar time. These biological systems’ rhythmic oscillations affect our daily lives and govern many of our habits and behaviors. When the biological rhythms are in the best position, athletes often achieve their best reaction time, mental performance, central temperature, and muscle performance.
The hormonal response to CR can also affect sports performance. For example, cortisol and testosterone levels are high in the morning and immediately before sleep and are lower during the day. These hormones affect athletic performance and can lead to improved or unsatisfactory performance.
About this study
The current study provides a comprehensive overview of the role of CR in athletic activities. The underlying mechanisms of CR in sports performance and the reverse link between CR, endocrine homeostasis, and sex differences were also described using a narrative synthesis of existing literature. The unique role of the circadian clock in physical performance and coordinating immune system function was also assessed.
A thorough search was conducted in Scopus, PubMed, and Web of Science databases using the keywords “sports performance,” “circadian rhythm,” “hormonal regulation,” “immune system,” and “injury prevention.”
Studies published in English and peer-reviewed journals until July 2023 were included. Studies analyzing the role of CR in hormonal status, sports performance, immune system function, and injury prevention in athletes were also included in the review.
The body’s core temperature is lowest in the morning and progressively rises during the day. Elevated body temperature promotes the use of carbohydrates as an energy source rather than fat.
The best performance of key indicators of sports performance is mainly in the afternoon. The actions during the evening happen roughly at the peak of core body temperature.
Seven additional variables explain the role of CR in exercise performance, of which include nutritional status, flexibility, sleep inertia, training times, time between test sessions, physiological responses, and motivation.
The endocrine rhythms and CR are closely related, with the internal clock influencing how the body responds to environmental factors. Previous research has also demonstrated that the circadian clock strictly regulates the immune response. CR also affects immunity, as demonstrated by ongoing changes in immune cell traffic in the blood.
Athletes are conscious of the value of training time in achieving desired results. For example, higher performance has been observed in the late afternoon. Rather than the day of the week, the time of day influences the body’s physical response to a greater extent.
Sleep is also essential, as adolescent athletes who sleep less than eight hours a night have been associated with a greater risk of injuries than their well-rested counterparts. During sleep, the released growth hormone plays a vital role in tissue regeneration and restoration.
The current review did not include studies on the signaling pathways affecting the CR. Likewise, the molecular and protein mechanisms influencing the CR were not thoroughly investigated.
The literature stresses clarifying the mechanisms behind the differences in exercise performance during the day; however, different training models should be examined to clarify the training differences.
Additional research is also needed to determine the effect of nutritional interventions on CR using appropriate methods to measure the impact of potential interventions.
Taken together, the current study demonstrates that an individual’s chronotype and exercising at specific times of the day are effective ways to significantly impact physical performance capabilities.
- Nobari, H., Azarian, S., Saedmocheshi, S., et al. (2023) Narrative review: The role of circadian rhythm on sports performance, hormonal regulation, immune system function, and injury prevention in athletes. Heliyon 9(9). doi:10.1016/j.heliyon.2023.e19636