Circadian health

Circadian rhythm and athletic performance

You are measurably stronger and faster in the late afternoon than at dawn, and the gap follows your internal clock, not your resolve. That same clock can be wrecked by a red-eye flight or a bright bedroom, and the cost shows up in points, rebounds, and games. Light is the lever that resets it. The trouble is that the dose deciding whether you adapt or stay jet-lagged is one no athlete can feel in a strange arena or hotel.

The connection

Athletic performance keeps a daily rhythm. Muscle strength, power output, reaction time, and core body temperature all peak in the late afternoon to early evening and bottom out in the early morning. The circadian clock runs that rhythm, and light sets the clock.

Cross enough time zones and the clock falls out of sync with the local schedule, and performance drops in ways you can measure. The cleanest tool for re-syncing it is well-timed light. Since the clock answers to melanopic light, measuring melanopic lux lets an athlete dose light on purpose instead of guessing in a strange arena or hotel, where the eye is useless for the job; a phone app like Wavelength reads that number off an iPhone.

The science

The time-of-day performance curve rides on core body temperature. In elite rugby sevens players, West et al. (2014) clocked core temperature rising from 36.92 C in the morning to 37.18 C in the afternoon, with lower-body peak power climbing alongside it from 5248 W to 5413 W, the two tightly correlated. Warm muscle is more pliable, fires impulses faster, and makes more force. And it is not only passive warming: recent work shows the muscle carries its own circadian clock (Douglas, Hesketh and Esser, 2021).

Light striking melanopsin-containing retinal cells sets the master clock. Khalsa et al. (2003) mapped the human phase response curve: light before the temperature minimum delays the clock, light after it advances the clock, the foundation under every light-timing protocol used against jet lag.

Light also acts fast, apart from any clock shift: daytime bright light raises alertness and cuts sleepiness (Lok et al., 2018). Evening light does the reverse to melatonin. Gooley et al. (2011) found ordinary room light before bed suppressed melatonin by more than 50 percent and trimmed the nightly melatonin window by about 90 minutes. For an athlete, that shorter biological night is recovery time lost.

What the research shows

The clearest field evidence comes from pro sport. Winter et al. (2009) combed 24,121 Major League Baseball games over ten seasons and found the team with a circadian edge from time-zone travel won 52.0 percent of games, rising to 60.6 percent with a three-time-zone edge.

The NBA shows the same eastward penalty, even sharper. Leota et al. (2022) analyzed 11,481 games: home teams hit with eastward jet lag lost roughly 6 percent of their winning percentage and surrendered significant points differential, rebounds, and shooting efficiency, with a 2-hour eastward shift costing 4.53 points of differential. Westward jet lag did no measurable harm. It fits the biology: eastward travel demands advancing the clock, which is harder and slower than the delay westward travel asks for.

Because the problem is clock alignment, the fix is clock realignment, and timed light is the most powerful tool on hand. Consensus guidance for athletes (Janse van Rensburg et al., 2021) builds its light advice on the phase-response principle: chase bright light in the new-zone morning to advance after flying east, and chase light later in the day after flying west.

Frequently asked questions

References

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Wavelength is a wellness and education tool, not a medical device. This page summarizes published research and is not medical advice. Consult a qualified clinician about any health condition or before starting light therapy.