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Pearls and Pitfalls

Body Clocks, Jet Lag, and Sports Performance: The Times of Our Lives

Eichner, E. Randy MD, FACSM

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Current Sports Medicine Reports: January 2020 - Volume 19 - Issue 1 - p 1-2
doi: 10.1249/JSR.0000000000000676
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Blame it on Thomas Edison. Until he came along, we were doing fine. We rose with the sun, worked by day, and slept by night. We were in harmony with our world. Then Edison, who needed only four hours of sleep a night, invented the electric light bulb. Soon thereafter, someone had to invent the alarm clock. And we have not been the same since.

Today, it is easy to get “out of sync” with our world. This has implications for health and sports. As our planet rotates to create a day-night cycle, we have a tiny body clock (rumored to be in the hypothalamus) that follows that cycle. This inborn “circadian rhythm” seems to orchestrate most of our biological functions, including sleep, mood, metabolism, temperature, alertness, vigor, heart rate, blood pressure, bronchial caliber, urine excretion, and hormone output. As we wax and wane in these vital functions, our sports performance may wax and wane in concert. This field of study—body clocks and sports performance—is sweeping and nuanced, but let me offer a few examples that seem relevant for athletes.

Body Clocks in Action

In a research study, two soccer teams aimed to play for 100 straight hours with brief rests but no sleep. In this marathon 4-day game, peak action was always at 5 p.m. and least action at 5 a.m. The exhausted players finally quit after 92 hours, just before 5 a.m. (1).

Pearl: From 3 a.m. to 5 a.m., your blood pressure is at its lowest, your pulse at its slowest, your bronchial caliber at its narrowest, and your body temperature at its coldest. From the age-old “circadian point of view,” in these wee hours of the morning, you were meant to be in your dark cave asleep, not out playing soccer under the flood lights.

Many studies find circadian rhythms in aspects of physical performance, including in leg, arm, and back strength; in jumping tasks; in sprint and anaerobic efforts; in aerobic tasks; and in sports such as soccer, cycling, and swimming (2). Even studies that fail to find circadian effects, as in certain cycling trials, are countered by other studies that find robust circadian effects, wherein cycling performance is worse in the morning, even in athletes who tend toward “morningness” in their chronobiology (3,4).

As for swimming, a study of 25 highly trained swimmers, young men and women, was well controlled for variables other than circadian rhythms. Subjects were studied during 50 to 55 hours in a laboratory on an “ultra-short” sleep-wake cycle. Each performed six 200-meter swim trials across eight times of day. Significant circadian variation occurred: Performance peaked at 11 p.m. and declined between 2 a.m. and 8 a.m. Performance tracked with body temperature—when the swimmers were warmer, they swam faster. Mood also mattered—when they felt less fatigue and had more vigor, they swam faster. Mean circadian variation from best to worst was nearly 6 seconds (5). Pearl: Your body clock can help you win a race.

Jet Lag Raises Its Ugly Head

The study of jet lag and sports performance is just as complicated and nuanced as the study of body clocks and performance. Airline travel, after all, can involve more than just jet lag and disruption of body clocks and circadian rhythms. It also can involve sleep deprivation, dehydration, medication, and changes in diet and/or altitude. All these may affect athletic performance.

Yet studies of jet lag continue to appear, and the field is fun to follow. Most pundits say that jet lag more commonly strikes on eastbound trips than on westbound, because eastbound flights “shorten the day” whereas westbound flights “lengthen it,” and it is easier to stay up late than to go to bed early. Conventional wisdom or folklore also holds that jet lag symptoms are worse on the second day after a trip than the first; that women, extroverts, and night owls have less jet lag than their counterparts; and that oldsters have more jet lag than youngsters. This for sure: Jet lag is highly subjective and individual. As one wag said: “I never heard anyone complain of jet lag on a Caribbean vacation.”

If “body-clock betting” is for you, bet on the West Coast team on “Monday Night Football.” Two studies find that, at home or away, West Coast teams have the edge, maybe because game time is closer to when they train. Similar trends occur in basketball. In a study of 101 National Basketball Association games where the visiting team flew cross-country, visitors scored 4 points more coming east than west. Why? Maybe because the night game is “earlier” on the body clocks of the eastward visitors (5). Pearl: For betting on a night game, when all else is equal, west is best (5).

Jet lag also has been studied in Major League Baseball (MLB). Here it gets confusing. In MLB, it seems, west is not best. In a study of East Coast versus West Coast teams, “home field advantage” was enhanced if the visiting team had just traveled east, but not west. In other words, only the West Coast MLB teams faced a “double handicap” of playing away games after eastward travel – they gave up more than one additional run in every such game (6).

A recent study of more than 40,000 MLB games keeps me guessing. The authors analyzed specifics of offensive and defensive play for home and away teams after east or west travel. They agreed with the older MLB study that “jet-lag effects” on wins and runs scored were “stronger after eastward travel.” They conclude that most of these effects, for both home and away teams, were explained by a single measure, home runs allowed. They blame pitchers more than they credit sluggers. They speculate that the away team may have a more structured daily schedule when away from home than the home team has when returning home. Their advice was that a starting pitcher for a game in which the team will be jet lagged might travel to the game site a few days ahead of the team, to adjust to the time zone (7). Pearl: Beats me. To quote columnist George Will: “Baseball, it is said, is only a game. True. And the Grand Canyon is only a hole in Arizona. Not all holes, or games, are created equal.”

In the Quest to be Best, Go West

Before I could fathom these MLB studies, another study hit my desk. This study was on jet lag, sleep, and team-sport performance. Ten fit young men were tested before and after outbound (west) and return (east) air travel between Australia and Qatar. The tests included jumping, sprinting, and the Yo-Yo intermittent recovery test (running 20 meters back and forth, with 10-second active rest periods; going ever-faster, until exhaustion). These tests are commonly used to gauge fitness for team sports such as soccer. Sleep also was measured, as was individual perception of jet lag, motivation, exertion, and physical feeling. Like other studies in this field, this study is complex and nuanced, and it lacks a counterbalanced design. But it agrees with most prior studies: Eastward travel takes a greater toll on athletes than westward travel. Specifically, this study shows greater detriment of east travel on sleep, subjective jet lag, fatigue and motivation, and intermittent sprint performance, particularly during the first 2 to 3 d after arrival. Granted, these researchers did not measure actual team-sport play. They hope, however, that their results convey novel information to coaches and athletes on the timeline of recovery for top team-sport play after east and west long-haul travel (8).

Finally, as for useful advice, a pioneer and esteemed researcher in this field, Thomas Reilly, has written an article full of solid information and detailed practical tips on how athletes can cope with jet lag (9).


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9. Reilly T. How can travelling athletes deal with jet-lag? Kinesiology. 2009; 41:128–35.
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