Brad asks: I am always nauseous after running marathons. After my last two marathons, I vomited 30 minutes after finishing. I drink water at most of the water stops and fuel along the way. What could be the cause?
I have seen runners with this problem at the finish of a marathon. To make an assessment for you, I would need a bit more history, but here are my thoughts on your problem.
There are basically two causes of vomiting: disturbances in the gastrointestinal (GI) tract and disturbances in the central nervous system (CNS). The common CNS disturbances in sport are concussion (not common in runners), exertional heat stroke, and exercise-associated hyponatremia (excess fluid intake).
Based on the description of your symptoms, it seems unlikely you have suffered from heat stroke. You could have a touch of hyponatremia, but that would imply that you took in enough water to exceed your weight losses (both fluid and glycogen stores) from running. This would be rare if you just drank at aid stations when you were thirsty. But it can happen if you overdid it at each station, and the amount of water you drank exceeded your fluid losses.
The GI system can be affected by running. The demands of running can cause reduced blood flow to the GI tract so that more blood is available for oxygen, nutrient, metabolic by-product, and heat transport to and from your muscles. In this situation, the fluid you ingest may not be well absorbed, which could result in you losing those fluids after the race.
If you are a very heavy sweater and you lose enough fluid while running to drop 4 percent of your body weight, some studies suggest that the gut stops absorbing fluid, you become nauseated, and eventually vomit. This is especially true for those who are dehydrated before they start to replace fluids during exercise.
There are some people who vomit following intense exercise, especially when it is more extreme than your body is accustomed to. I can remember “tossing my cookies,” as coach would say, after line drills in early season hockey practices. This could happen to you if you really pushed the last mile or two of the marathon.
My general advice for you is to start with checking your pre-run and post-run weight to get a feel for your sweat losses. You need to be careful to not exceed your sweat losses with unnecessary fluid replacement. A general rule of thumb is to just drink when you are thirsty. Do not push fluids when racing.