Collapsing after a race: dehydration or blood pooling?


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Watch the finish line at big endurance races, and you’ll see plenty of people staggering to a halt and then wobbling, looking dizzy, and perhaps even collapsing if race volunteers don’t get there in time to usher them to the medical tent. What’s going on here? Why are they collapsing after the race, and how should they be treated? A new paper posted online at the British Journal of Sports Medicine takes a look at the two leading theories: (1) they’re dehydrated and overheated, or (2) the blood vessels in their extremities are dilated, so when they stop exerting themselves, the blood pools there and leads to shortage of blood going to the brain.

The right treatment depends on which of those theories you believe. If it’s dehydration, you give IV fluids. If it’s blood pooling, you put the athlete in the “Trendelenburg position” (lying down with legs elevated above heart) and let them drink as much as they want. Researchers from the University of Cape Town conducted a randomized clinical trial at the 2006 and 2007 South African Ironman Triathlons and the 2006 Comrades Marathon, randomly assigning 28 collapsed athletes to the two treatment protocols based on whether they had an even or odd race number.

The results: no statistically significant difference between the protocols: 52 minutes before discharge for the IV group, 58 minutes for the non-IV group, with a standard deviation of 18 to 23 minutes. So this doesn’t really settle the debate about what’s causing it — but, applying the “simple is better” principle, it suggests that you don’t really need an IV if you’re dizzy at the end of a race (but don’t have, say, a temperature above 40C).