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

Background

CRs are day by day shifts in biological and behavioral activity on account of an organism’s natural capability to synchronize with the environment’s 24-hour cycle of sunshine and darkness. CRs originate from the body’s biological clock that regulates many elements, akin to 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 day by day lives and govern a lot of our habits and behaviors. When the biological rhythms are in one of the best position, athletes often achieve their best response time, mental performance, central temperature, and muscle performance.

The hormonal response to CR may also affect sports performance. For instance, cortisol and testosterone levels are high within the morning and immediately before sleep and are lower through the day. These hormones affect athletic performance and might result in improved or unsatisfactory performance.

About this study

The present 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. 

An intensive 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 within the review.

Key findings

The body’s core temperature is lowest within the morning and progressively rises through the day. Elevated body temperature promotes using carbohydrates as an energy source somewhat than fat.

One of the best performance of key indicators of sports performance is principally within the afternoon. The actions through the evening occur roughly at the height of core body temperature.

Seven additional variables explain the role of CR in exercise performance, of which include dietary status, flexibility, sleep inertia, training times, time between test sessions, physiological responses, and motivation.

The endocrine rhythms and CR are closely related, with the interior clock influencing how the body responds to environmental aspects. 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 within the blood.

Athletes are conscious of the worth of coaching time in achieving desired results. For instance, higher performance has been observed within the late afternoon. Reasonably than the day of the week, the time of day influences the body’s physical response to a greater extent.

Sleep can also be essential, as adolescent athletes who sleep lower than eight hours an evening have been related to a greater risk of injuries than their well-rested counterparts. During sleep, the released growth hormone plays an important role in tissue regeneration and restoration.

Conclusions

The present review didn’t include studies on the signaling pathways affecting the CR. Likewise, the molecular and protein mechanisms influencing the CR weren’t thoroughly investigated.

The literature stresses clarifying the mechanisms behind the differences in exercise performance through the day; nonetheless, different training models must be examined to make clear the training differences.

Additional research can also be needed to find out the effect of dietary interventions on CR using appropriate methods to measure the impact of potential interventions.

Taken together, the present study demonstrates that a person’s chronotype and exercising at specific times of the day are effective ways to significantly impact physical performance capabilities.