Post-exercise nausea can be brought about by a large number of things. But the root cause can usually be traced back to some kind of basic disturbance of homeostasis (the body’s preferred, stable internal status) and the following are a few common culprits:
1. Unaccustomed exercise intensity. In other words, if you go really hard during a session or race and you’re not conditioned for it, this can leave you feeling rough. Being gently progressive in your workouts and training very specifically for the demands of racing are the best fix.
2. Screwing up your nutritional intake. Either eating too soon before exercise, eating too much or eating way less than you need to are all common causes of feeling sick during or immediately after exercise. To combat this you need to work on improving your nutrition plan and trying out some different strategies until you figure out what works for you.
3. Over-hydration. If you over-drink, especially plain water, during exercise, nausea can be a sign of impending hyponatremia (low blood sodium levels) so don’t be too aggressive with fluid intake and take some electrolytes (sodium in particular) if you have a high sweat rate.
4. Overheating. Sickness can also be a sign of a large rise in core body temperature. Pacing yourself and employing tactics to keep cool obviously help and are necessary if you’re training and racing in the heat and prone to sickness afterwards.
Of course, there can be other issues leading to post-exercise sickness such as ingesting bugs or bacteria (common in triathlon if the swim is in poor quality water), but the above checklist is a good place to start if this is regularly happening to you.
Sports scientist Andy Blow is a former top Ironman and founder of Precision Hydration, which specialises in tailored sports hydration