Why Do We Yawn When We Exercise?

Originally posted here: https://mcgill.ca/oss/article/did-you-know-health-general-science/why-do-we-yawn-when-we-exercise

For a while I thought I was the only one trying to ‘swallow my head’ (as my Nana used to say) while running, but a google search today told me I wasn’t alone. Many people suffer from the constant yawning I experience as soon as I do anything remotely physically active, from running to biking to even walking uphill. So why do we yawn when we exercise? Why do we yawn at all?

Well, yawning is a touch of a mystery. Even fetuses can experience yawns (click here to see that), though I’d doubt they’re doing so due to physical activity.It was once thought that animals yawned to increase the oxygen in their bodies, especially in their brains, but studies giving patients more or less oxygen found it did not effect the frequency of yawning. It is also theorized that yawning is used to keep organisms alert, an idea that explains why yawns are contagious- to remind other nearby animals to stay alert as well. In some animals, notably dogs, yawns are used to communicate anxiety or nervousness.

Another theory is that yawning is another way for bodies to thermoregulate, via the action of neurotransmitters. Serotonin is an important neurotransmitter in the regulation of skin blood flow, and the thermoregulation this blood flow does. Increases of serotonin have been shown to increase body and brain temperatures, a change that causes the body to trigger more yawns, in an attempt to cool itself. The effects of serotonin on thermoregulation are especially obvious in the case of patients who suffer from serotonin syndrome, a condition caused by an excess of serotonin in their systems, usually from taking several serotonin-affecting drugs in tandem. Some of the biggest signs of serotonin syndrome are hyperthermia, shivering, sweating and vasoconstriction. This process is also obvious to SSRI (selective serotonin reuptake inhibitor) or SNRI (selective serotonin and norepinephrine reuptake inhibitor) users who experience a relatively (~11%) common side effect of the medications- excessive yawning. While the users may not be aware of it, the increased serotonin levels in their body increases its temperature, and therefore it’s yawn rate. Case studies have shown patients to experience as many as 200 yawns per day! 

Less innocently however than heat or medication induced yawns are yawns as a clinical symptom. The main reason we yawn consciously is to relieve pressure in our skulls, like when you try to ‘pop your ears’ on an airplane, so an increased rate of yawning can be a body’s attempts to relieveintracranial hypertension (too much pressure on the brain), migraines, or even heart or kidney problems. So if you’re not warm, taking SS/SNRIs, sleepy or anxious, and are experiencing excessive yawning, it may be worth mentioning to your doctor. Finally at least my mystery is solved; Run fast, get warm, start yawning. Maybe I should try running in the winter? 

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