The more intense your session, the more lactate your body produces, says Helen Kollias, Ph.D., Toronto-based director of science for Precision Nutrition. Both byproducts make your body more acidic, a change that can lead to the above symptoms. In extreme cases, you may throw up as your body tries to relieve itself of the acidity.
One easy way to minimize the nausea: Walk or bike at a low intensity for at least 10 minutes after your session. Cooling down boosts blood flow and gives your body the chance to convert lactate into energy, thereby lowering acidity, Kollias says. Hydrating can also help. Aim to drink 150 percent of the water you lost during your workout; your urine should be pale yellow.
The bottom line:
You’re most likely to experience these reactions after total-body HIIT workouts, Kollias says. Instead of skipping post-workout fuel altogether, take in fluids and simple carbs (like fresh juice or rice, which are easy to digest) until your stomach settles.