The Impact of the Circadian Rhythm on Athletic Performance

Daniel Jabr

The Impact of the Circadian Rhythm on Athletic Performance

Dr. Daniel Cavanaugh of Loyola University Chicago presented a talk this semester overviewing the circadian rhythm and his research in the field.

The circadian system is an endogenous timing mechanism that allows organisms to adapt to environmental stimuli by synchronizing physiology and behavior in anticipation of environmental change. The circadian system is ubiquitously found in organisms from bacteria to humans, reflecting the essential role the system has on survival. This system consists of three components; input pathways, the core clock, and output pathways. Input pathways relay environmental stimuli such as temperature, light, and food availability to the core clock. The core clock is a population of neurons called clock cells that contain a molecular clock that tracks time with a cycle of approximately 24 hours. Output pathways couple the clock cells to behavioral and physiological changes that generate circadian rhythms in diverse processes including locomotor activity, feeding, sleep, hormone release, and body temperature, among other outputs.

As such, this mechanism allows the organism to adapt to the environment, as physiological parameters oscillate daily with a circadian pattern to promote different activities of the organism. For example, at night, the circadian system drives sleep.

Hormone release, blood pressure, and body temperature, are all processes that fluctuate daily with a circadian pattern. One hormone of note that is under circadian control is cortisol. Cortisol is a steroid hormone released by the adrenal cortex in response to stress and regulates various aspects of metabolism and has anti-inflammatory qualities and increases alertness. This hormone is under circadian control, where the levels of circulating cortisol peak in the morning around 9:00 am and reaches its lowest levels at midnight. Thus, the highest level of alertness is in the early morning, following the surge in cortisol. Cortisol is just one example of a circadian factor that impacts alertness, but there are many other factors that function to contribute to peak alertness and peak physical ability. So, this precise timing of circadian factors contributes to peak physical and mental performance throughout the day whereby at some points in the day, people are more likely to perform better at athletic or mental tasks due to the surge in factors from the circadian system.

This realization that performance is influenced by the circadian rhythm has become a focus of research. Researchers have looked at the effect of travelling across time-zones on physical performance. When travelling across time-zones, the circadian clock becomes misaligned with the external time meaning that the timing of the rhythm is not synchronized to the external environment, as the person is now exposed to a new time zone. Thus, this has implications to many sports teams, as travelling across the US to play games constantly shifts the external environment and produces a misalignment. Does this misalignment have any impact on the success of teams?   

Roy et al. (2018) investigated the effects of circadian misalignment in three US sports leagues: the NBA, the NHL, and the NFL. The researchers analyzed 5 years’ worth of games for each league and analyzed the winning-ness of the visiting team with respect to how many time-zones they travelled and the time of day the game was played. They used statistical measures to analyze the data. For all three leagues, they found that when visiting teams were travelling westward and played a game at night, they had a huge disadvantage. They found NBA teams travelling across one time zone moving westward had a 33.1% winning percentage, while an NBA team moving one time zone eastward showed a 47.6% winning percentage. The western moving team had a much lower winning percentage then the east. Travelling westward, the players are getting less exposure to the sun as they are travelling in the direction that the sun is setting. Sunlight drives the circadian system to synchronize the clock with the external environment, as sunlight hits the eyes and the eyes stimulate the clock in the brain to adjust the timing of the clock. Thus, the players moving to the west have less exposure to the sun and therefore their circadian system is less able to synchronize the clock to the external environment, leading to misalignment that leads to decreased physical performance. For both eastward and westward travelling teams, they are experiencing winning less then 50% of the time when playing at night. This is because the players have to play at a time when their circadian system is slowing down alertness and preparing the body for rest and sleep leading to a gross decrease in alertness and physical performance, with the decrease being particularly prominent for westward travelling teams due to the lack of sunlight. Thus, the timing of games and the travelling of teams has an impact on the chances the team will win the game.  

These results highlight the importance of the circadian rhythm on physical performance and sports. Furthermore, circadian rhythms have become a prominent concern for travelling teams. Teams have begun to orchestrate specific schedules to minimize circadian misalignment and time the clock to be more alert at night by sleeping to the schedule of the time zone they are going to be travelling to. Icons of sports such as LeBron James and Michael Phelps have implemented specific schedules to maintain their circadian system by specifically timing sleep, meal times, exercise, and other activities to ensure peak athletic performance. Thus, sports teams are beginning to realize the importance of the rhythm and are implementing schedules to improve performance.  

Link to the journal article: http://onlinelibrary.wiley.com/doi/10.1111/jsr.12565/full

References:

Roy, J, Forest, G. 2018. Greater circadian disadvantage during evening games for the NBA, NHL, and NFL teams travelling westward. Journal of sleep research 27:86-89

Boivin, D, Duffy J, Kronauer, R, Czeisler C. 1996. Dose-response relationships for resetting of human circadian clock by light. Nature 379:540-542

Baron, KG, Reid, KJ. 2014. Circadian misalignment and health. International Review of Psychicatry 26:139-154