September 1, 2020
Written by: Sarah Reitz
Elite athletes are trained to compete at their highest level regardless of external factors, like a crowd booing loudly or a surprise rain storm. While the types of challenges facing each athlete can depend on the sport, or even the team, there is one challenge to their performance ability that all athletes must contend with: their circadian rhythm.
What are circadian rhythms?
A circadian rhythm is any process that fluctuates with a period of roughly 24 hours. While sleep and wake cycles are the most common examples of circadian rhythms, there are many other examples of behavioral and physiological processes that regularly fluctuate over each day. For example, body temperature, blood pressure, release of certain hormones like cortisol, and eating and drinking schedules all show 24 hour rhythms in humans (1).
The exact timing of an individual’s circadian rhythm depends on both internal and external factors. Internal factors such as genetics may predispose someone to be more of a morning or an evening person, while external factors such as light exposure and general lifestyle are also known to strongly influence the timing of the rhythm.
However, all of these influences are integrated by the “master clock” of the body: the suprachiasmatic nucleus (SCN). The SCN is found in the hypothalamus (Figure 1), and receives input from all over the brain (1). Using this information, this tiny bundle of neurons controls all of the circadian rhythms in the body, making sure they are synchronized with each other as well as with the external environment. It does this using a combination of electrical communication with other regions of the brain and hormone signals that are capable of traveling outside the nervous system and reach the rest of the body (1).
How does athletic performance change across the circadian rhythm?
Elite athletes with years of intense training shouldn’t be affected by the time of day though, right? As it turns out, circadian rhythm can have a significant effect on athletic performance in many sports. But how does athletic performance change across the day, and what times of day does peak performance tend to occur?
Many studies report that performance in a variety of sports is higher in the afternoon and early evening compared to the morning. For example, the accuracy of serves in both tennis and badminton is higher in the afternoon than in the morning (2). 20m sprint times and 16km cycling performances are also higher in the evening (3,4). One general trend seems to be that performance in sports involving technical skills, such as soccer and tennis, peak earlier in the afternoon compared to sports involving more muscle strength and anaerobic activity, such as swimming and sprinting (2).
Some researchers believe this increase in performance later in the day may be linked to body temperature circadian rhythms. Swimming performances in 100m and 400m races, in which the water is held at a constant temperature, are still improved in the afternoon and early evening, when body temperature is naturally the highest, compared to the morning (5). Circadian changes in muscles are also likely involved, as peak flexibility as well as muscle strength occurs in the early evening (4).
What happens when the circadian rhythm is disrupted?
At the college and professional level, extensive travel across time zones is often required in order to compete against athletes from across the country and the world. While plane travel now allows teams to fly halfway across the world in less than a day, the brain cannot synchronize the body’s internal circadian clock to the new time zone that quickly. Knowing how much of an effect circadian rhythm can have on athletic performance, what happens when this rhythm is disrupted?
Traveling to a new time zone often results in a condition known as jet lag, which includes symptoms such as fatigue, headache, difficulty sleeping, and loss of concentration. Symptoms of jet lag can persist until the brain and body are fully adjusted to the new time zone, which usually occurs at a rate of 1 day for each time zone crossed (2).
One way researchers can study the impact of jet lag and circadian rhythm disruption on athletic performance is to examine archival data from various sports when teams from different time zones competed against each other. In general, they found that teams traveling eastward to compete were more likely to have impaired performances or lose compared to teams traveling westward (6-8). This is likely due to the fact that competitions occur in the late morning or early afternoon, prior to the circadian peak of the western team but right near the circadian peak for the eastern team.
One exception to this is when competitions occur late at night local time. One study examined 25 seasons worth of Monday night NFL games to see if time zone and circadian rhythm affected performance. Because these games start around 9pm Eastern time, the teams from the East Coast were always playing much later than their optimal circadian time, which is closer to 5pm. However, this means that these games occurred right at the circadian peak of athletes from West Coast teams. In these cases, the western teams won more often and by more points. This effect was so dramatic that using circadian rhythm to predict the winner was more accurate than Las Vegas odds (9)!
How can athletes combat circadian effects on performance?
Knowing the impact circadian rhythms can have on the outcome of competitions, teams are now looking for ways to combat these effects and use circadian influence to their advantage. In a perfect world, athletes would be able to spend one day in the competition location for every time zone crossed traveling to the location to allow their internal clocks to fully synchronize with local time before the competition. However, the schedules of many athletes do not allow for this type of time before every game.
Instead, many teams now work with sleep physicians to develop protocols that allow players to compete at their circadian peaks. These physicians take advantage of the fact that neurons in the SCN are connected to the retina of the eye. These connections mean that circadian rhythms entrained by the SCN can be altered by exposure to bright light, where bright light shifts rhythms to the more “alert” phase of the rhythm (1). Though not as powerful as light, the timing of sleep and meals can also SCN activity, shifting circadian rhythms to match these environmental cues. Therefore, by adjusting light exposure and sleep schedules for the days leading up to travel, athletes can artificially shift their circadian rhythms such that their peak circadian performance time will occur at the local competition time (10).
Another way athletes can take advantage of circadian rhythm influences is by raising their body temperature to mimic evening circadian conditions prior to competitions that take place in the morning. Work has shown that active warm-ups in the morning, which increase body temperature to evening levels, also increase performance in certain activities to evening levels, essentially eliminating the circadian effects on performance (11). Another study suggests that this circadian difference in morning and evening performance may also be eliminated by regularly training at both times of day (12).
When evaluating the data from circadian rhythm studies, the effects of these rhythms on athletic performance can seem trivial. However, in the world of sports, the smallest change in speed, accuracy, or strength can mean the difference between winning and losing. As scientists learn more about circadian rhythms and exactly how the SCN integrates such a vast array of information to control these rhythms, perhaps we will see even more consideration of these rhythms in sports teams at all levels.
Image References:
Cover Image: Image by Varun Kulkarni via Pixabay, https://pixabay.com/photos/basketball-sport-ball-game-2258651/
Figure 1: Image by Anatomography via Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Suprachiasmatic_nucleus.gif
References:
- Hastings MH, Maywood ES & Brancaccio M (2018) Generation of circadian rhythms in the suprachiasmatic nucleus. Nat Rev Neurosci 19, 453–469. https://doi.org/10.1038/s41583-018-0026-z
- Thun E, Bjorvatn B, Flo E, Harris A, Pallesen S (2014) Sleep, circadian rhythms, and athletic performance. Sleep Med Rev 23(2015)1-9.
- Rahnama N, Sajjadi N, Bambaeichi E, Sadeghipour HR, Daneshjoo H, Nazary B (2009) Dirunal variation on the performance of soccer-specific skills. World J Sport Sci 2:27-30.
- Drust B, Waterhouse J, Atkinson G, Edwards B, Reilly T (2005) Circadian rhythms in sports performance – an update. Chronobiology International 22(1):21-44.
- Baxter C, Reilly T (1983) Influence of time of day on all-out swimming. Br. J. Sports Med. 17(2): 122–127.
- Worthen JB, Wade CE (1999) Direction of travel and visiting team athletic performance: support for a circadian dysrhythmia hypothesis. J Sport Beh 22:279-87.
- Recht LD, Lew RA, Schwartz WJ (1995) Baseball teams beaten by jet lag. Nature 377:583.
- Chapman DW, Bullock N, Ross A, Rosemond D, Martin DT (2012) Detrimental effects of west to east transmeridian flight on jump performance. Eur J Appl Physiol 112:1663-9.
- Smith RS, Guilleminault C, Efron B (1997) Circadian rhythms and enhanced athletic performance in the National Football League. Sleep 20:366-9.
- Javierre C, Calvo M, Diez A, Garrido E, Segura R, Ventura JL (1996) Influence of sleep and meal schedules on performance peaks in competitive sprinters. Int. J. Sports Med. 17, 404–408.
- Taylor K-L, Cronin J, Gill N, Chapman D, Sheppard J (2011) Warm-up affects diurnal variation in power output. Int J Sports Med 32:185-9.
- Arnett M (2001) The effect of a morning and afternoon practice schedule on morning and afternoon swim performance. J Strength Cond Res. 15:127-31
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