Workouts should make you feel good, not like you're going to barf. But every now and then, when you're trying really hard to get a runner's high, or hoping to feel blissed-out after a hot yoga class, you may find that you're nauseous to the point of wanting or needing to puke. This is often referred to as "exercise-induced nausea and vomiting," and there are a few common reasons why it strikes.
Most people assume that getting queasy during a workout means you're working hard, but that's only partially true — a 2002 study suggests that athletes experience nausea when they exercise at 75% of their VO2 max, which is a measurement of the maximum amount of oxygen your body uses during aerobic exercise. But that doesn't mean that nausea is a sign of a good workout. Basically, intense exercise interferes with digestion, which can sometimes make you feel like you have to vom.
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During a workout, blood flows to the muscles that are working, and therefore away from the organs in your digestive system. As a result, your gastrointestinal tract has a harder time doing its job, and it takes longer for your stomach to "empty" foods into your intestines. This can lead to a handful of uncomfortable symptoms, including nausea or diarrhea. Running in particular tends to trigger these GI disturbances, because your body is also literally shaken up in a way that can speed up gut motility. And if you ate less than three hours before working out, then it can also exacerbate symptoms even further and make your stomach feel worse.
Beyond GI issues, sometimes nausea and vomiting during exercise can be a sign of heat stroke. According to the American Council on Exercise, the best temperature for working out is between 68 and 72 degrees Fahrenheit, and anything above 80 degrees can be dangerous. If you notice any other symptoms of heat stroke, like confusion, changes in sweating, or a core body temperature above 104 degrees, then it's important to get in a cool area and seek medical assistance immediately.
So, what can you do to make sure that you're not barfing during your next spin class? Well, staying hydrated is one great way to keep blood flowing in the right places, prevent heat illnesses, and help recover after a tough workout. But if you start to feel nauseous and you're already in the midst of a workout, then it's a good idea to dial back your intensity, and take a break until you feel better — which can take hours if you're waiting for your core body temperature to come down. Definitely resist the urge to push through the nausea, because that will only make you feel worse. Feeling nauseous during exercise is normal regardless of your fitness level, so it's not a sign that you're out of shape either.
And remember: the only thing you should feel after a workout is happy, and maybe a little bit sore.