Ultramarathons can induce physiological crapstorms. You don’t need a study citation for that statement, especially if you’ve ever seen post-race urine samples. I have seen a few pee cups after hot, grueling ultras (don’t ask), and they could serve as the set location for the next big game show: “Coca Cola, Tomato Soup, Or Urine?” In my fantasy, Bob Barker comes out of retirement to host.
The brown urine that some athletes experience after hard ultra events (especially those in heat) is an extreme example of post-race physiological breakdown. The brownish tint may be severe dehydration, mixed with the byproducts of muscle damage. Red is especially dangerous and hopefully rare, possibly indicative of blood (or pre-race beets). Sometimes it comes with pulp, and you don’t want to know what that is.
One of the most eye-opening studies I have ever seen was published in 2012 in the Wilderness Environmental Medicine journal. At the Western States 100 in 2010, 216 of 328 finishers underwent a post-race blood test to measure creatine kinase, an enzyme found in skeletal muscle, used as a proxy for muscle breakdown. The reference range goes up to 198 units per liter. Many emergency rooms will admit patients (or refuse to discharge those receiving inpatient treatment) for levels above 5000 units per liter, especially if accompanied by symptoms of rhabdomyolysis. The average creatine kinase value of Western States finishers was 32,956 units per liter (many hospital tests don’t even measure above 30,000).