Lately, I’ve been watching clips from the Olympics, getting misty-eyed when the athletes hug at the end, and then stalking the winners on social media: a normal Saturday night in 2021. I have a shirt that looks like that, I think as I scroll through photos of them lifting approximately three times my body weight. We’re not so different, you and I, I think as they hit a five-inch target from a football field away.
Like with most things in my life, there’s a circadian science angle that’s jumped out at me as I’ve been doing this. Namely, for at least a couple of the U.S. contenders, their Instagram posts about “heading out to Tokyo” were happening… five days before their event.
This surprised me for the simple reason that international travel = jet lag = circadian disruption = presumably disrupted sleep and performance. And with Tokyo being 13 to 16 hours ahead of the US time zones, I’d expect our athletes to take at least 8 to 11 days to adjust. Of course, there are financial reasons why people can’t afford to travel to Tokyo a month ahead of time to fully adjust to the new time zone, but it still had me wondering: what were they doing with their light exposure to entrain during those five days? And how much of their performance could be explained by their circadian phase at the time they were competing?
Terminology time: Entraining is the process of syncing up with a new time zone, and “circadian phase” is another way of saying “what time their body thinks it is.” Two people in the same time zone can have different circadian phases at 2:00 pm if they typically follow different light schedules, and when you cross to a different time zone, odds are good that your circadian phase will be markedly different than everyone who’s been living there for months– at least, until you get adjusted.
The general rule of thumb for entrainment is that travelers shift about an hour per day, which means that delaying your clock by nine hours should take you about nine days. In our own work, we’ve found that you can shift faster than an hour a day by getting light at the right times and avoiding it at others, so that a nine hour shift can be achieved in 3-4 days. But it’s unclear how often travelers put schedules like this to work in the real world.
So, one thing Olympians should be aware of is that there are shortcuts that can help them adjust to a new time zone faster than they would if they simply tried to adopt their normal wake and bedtime routines upon landing in the new time zone.
But there’s another component to this too, which is that question of “what’s their circadian phase at the time they’re competing?” We know people tend to be best at physical performance in the early evening, which aligns with a peak in core body temperature. But this early evening guideline only applies to people who are entrained to their time zone. If you transplant me into a new time zone, my body’s “early evening” could be happening at 7:00 am local time, or noon, or 3:00 am in the morning. My body’s time at that point is (literally) all in my head.
In other words, there are two circadian goals you might have as an elite athlete crossing time zones. You’ll probably want to entrain as quickly as possible, to get over the disrupted sleep and general feelings of bleh that come from jet lag. But you might also want to entrain yourself to a schedule that aligns your body’s peak performance with the time you’re supposed to compete. Because if you’re supposed to lift weights at 10:00 am in the morning, you can probably give yourself an edge by tricking your body into thinking it’s really later in the day.
There’s data to back this idea up: In a neat 2020 paper from Lok et al., the authors looked at time-of-day effects in Olympic swim times from 2004 and 2016. Using local time as a proxy for internal time with the Olympics is a little tricky, in that we don’t know how entrained the athletes were at the time of the competition. But it’s good as a first-order approximation, since most of them had probably been on-site for at least a few days.
The researchers found that there were clear effects of time of competition on performance, with slowest swim times happening in the early morning and fastest swims in the late afternoon. These effects were big enough to exceed the difference between gold and silver in 40% of the finals, and between silver and bronze in 64% of the finals. Could some silver medalists have gotten gold just by shifting their circadian clock? This work seems to suggest that it’s possible.
There’s a lot of cool research to be done in this space, including actually trying to shift athletes in this way to see if it helps them on game day, and incorporating their individual chronotypes (morning lark, night owl) into the plans they follow. The nice thing is that we’ve written the code to create these custom lighting prescriptions already in our work on optimal strategies for shifting the circadian clock.
I guess what I’m saying is that if you’re an elite athlete reading this and you’re interested in shifting your circadian clock for optimal performance, call me. Or stalk me on Instagram first, then call me. We’re not so different, you and I.