With less sleep comes less energy for physical activity. No surprise there. But according to a recently released study published in Scientific Reports, (1) the effects of sleep deprivation on sports performance may be far more significant than originally thought, with performance heavily contingent on two factors: the alignment of your internal body clock (aka circadian rhythm) and the quality of your sleep. Here’s what you need to know.

About the study

An occupational health scientist at Oregon Health & Science University who specializes in sleep, Andrew McHill, PhD, found himself questioning why it is that professional sports teams tend to perform better when playing at home versus on the road. His hypothesis was that travel disrupts one's sleep schedule, which disrupts one's internal body clock which, in turn, has a significant impact on performance. But it was only when COVID hit and the NBA began operating in a bubble format (with all teams located in one place...in this case, Walt Disney World) that he was able to conduct a study that put his hypothesis to the test.

McHill and his colleague, sleep and circadian physiologist Evan Chinoy, leveraged this unique opportunity to compare the athletic performance of teams pre-COVID with that of the same teams playing in the no-travel bubble.

“The internal circadian clock dictates the daily timing of changes in physiology and behavior and has been found to impact even high-level activities such as athletic performance,” write McHill and Chinoy. “However, in modern society with the ability to easily travel across time zones, humans often initiate athletic activities at times when the internal clock may not be promoting optimal performance and thus could provide a benefit to the team that does not travel. While colloquially referred to as ‘home-court advantage,’ specific reasons for this advantage are often difficult to disentangle due to multiple variables pertaining to game-situations/travel occurring simultaneously (e.g., home-crowd noise, air-travel discomfort, time zone changes, etc.)...By creating a ‘bubble,’ the NBA generated a natural experiment whereby the impact of travel and time zone changes could be systematically teased apart.”

"Humans often initiate athletic activities at times when the internal clock may not be promoting optimal performance and thus could provide a benefit to the team that does not travel."

Andrew McHill, PhD + Evan Chinoy

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How athletic performance was measured

McHill and Chinoy identified several key factors that contribute to winning:

  1. Field goal percentage
  2. Free throw attempt rate (free throw/field goal attempt)
  3. Offensive rebounding percentage
  4. Turnover percentage (turnovers/100 possessions)
  5. Offensive rating (points/100 possessions)
  6. Defensive rating (points allowed/100 possessions)

Winning percentages before the “bubble”

Prior to COVID, when teams were traveling as usual, the average winning percentage for home games was 63.8% compared to 50.8% for away games.

Interestingly, the percentages differed depending on direction, with westward travel having a worse effect than eastward—which, when you think about it, makes sense. Most games begin around 7pm, so when the Brooklyn Nets play in Portland against the Trail Blazers, that’s effectively a 10pm start time, which is more disruptive to sleep patterns than a West Coast team traveling east.

Also worth noting is the fact that these numbers differed slightly depending on how many time zones the team had to cross, with the trend deemed “significant” for one or two time zones, “non-significant” for three time zones, and “not different” when remaining within their own time zone.

Winning percentages during the “bubble”

When playing within the bubble, teams were still assigned as “home” or “away” despite the fact that everyone was based in the same place with no travel or changing time zones (or fans). In this environment, there wasn’t a significant difference in “home” vs “away” winning percentages. Plus, the caliber of performance was higher.

“Everyone was shooting better,” explained McHill. “There was a lot more scoring. In any given game, you didn’t have one team that was shooting worse like you normally would.” (2)

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Additional supporting studies

While McHill’s research is notable due to the exceptional circumstances with which it was conducted, it’s not the first study to assess the relationship between sleep and athletic performance.

A study conducted at Stanford University (3) evaluated the relationship between hours of sleep and athletic performance of collegiate basketball players. Lead researchers Cheri D. Mah and Kenneth E. Mah asked 11 healthy students without sleep disorders on the men’s basketball team to maintain their normal sleep-wake schedule for 2-4 weeks in order to get a baseline for reaction time, levels of daytime sleepiness, and mood. What followed was a 5-7 week period of “sleep extension” in which they slept a minimum of 10 hours/night—representing an average increase of 110 minutes.

Results showed that, during the sleep time extension period, student athletes demonstrated:

  • Faster sprint times: 16.2 seconds at baseline vs 15.5 during sleep extension
  • Improved shooting accuracy: 9% increase in free throw percentage + 9.2% increase in 3-point field goal percentage
  • Improved overall ratings of physical well-being and mental health during practices and games

Basketball isn't the only sport that's been evaluated—tennis has as well. A 2015 study (4) considered the effects of sleep extension on the physical performance of college varsity tennis players, with results showing that approximately two hours of extra sleep per night significantly improved serving accuracy (35.7% vs 41.8%).

Interested in learning more about other ways lack of sleep affects performance? Read up on the surprising impact of sleep loss on cognitive performance/cognitive function and decision making.

Convinced you're getting enough sleep but still feeling tired and resorting to napping? Here are seven potential reasons why. And for tips on how to get better sleep, give one of these 16 science-backed strategies a try.