As soon as someone lets out a yawn, it spreads like wildfire across the room (and apparently just writing about yawning can set off the chain reaction as well). Traditionally, yawning has been an indicator of two things: boredom or fatigue. But yawning during exercise might actually be the brain’s version of an in-workout cool-down Yawning and stretching predict brain temperature changes in rats: support for the thermoregulatory hypothesis. Yawning and Stretching Predict Brain Temperature Changes in Rats: Support for the Thermoregulatory Hypothesis. Shoup-Knox, M.L., Gallup, A., Gallup, Jr, G., et al. Department of Psychology, University at Albany, Albany, NY. Frontiers in Evolutionary Neuroscience. 2010; 2: 108. .

The Yearn To Yawn — Why It Matters

Yawning was long thought to be an indication of low oxygen levels in the blood, but scientists have since dispelled that theory Yawning: no effect of 3-5% CO2, 100% O2, and exercise. Provine, R.R., Tate, B.C., Geldmacher, L.L. Department of Psychology, University of Maryland. Behavioral and Neural Biology. 1987 Nov;48(3):382-93. . Besides, if that were the case, runners, bikers, weightlifters, and athletes of all kinds would be yawning instead of panting during their workouts. There’s also another theory claiming yawning is a response to good old fashioned boredom, although mid-workout or in-competition yawns probably don't fit that bill.

Recent research, however, suggests yawning and stretching actually act as cooling mechanisms for the brain Yawning and stretching predict brain temperature changes in rats: support for the thermoregulatory hypothesis. Yawning and Stretching Predict Brain Temperature Changes in Rats: Support for the Thermoregulatory Hypothesis. Shoup-Knox, M.L., Gallup, A., Gallup, Jr, G., et al. Department of Psychology, University at Albany, Albany, NY. Frontiers in Evolutionary Neuroscience. 2010; 2: 108. . A study found that in rats, increased brain temperature occurred prior to spontaneous yawning, while brain temperature decreased post-yawn, signaling the body's attempt to lower its internal temperature. Yawning is a natural mechanism to open up airways, which increases air flow, cooling the brain.

Should We Put Yawning To Bed? — The Answer/Debate

While the cooling theory might make a lot of logical sense in the context of exercise, it's very much an unproven hypothesis in science. Basically the only thing certain about yawning is that there are many theories as to why it happens in a given situation.

Regardless of which theory ultimately wins out, assuming a person is well-rested (ruling out fatigue), a moderate amount of spontaneous yawning during a workout isn't out of the ordinary. However, if excessive, non-stop yawning interferes with a workout, check with a doctor, as it could be a sign of a heart or blood pressure condition.

But until there’s a solid conclusion, there’s no excuse available for inappropriate yawning in public.

Certainty Level

Kim Kardashian isn't sure what causes it, but she's made yawning in public kool.

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