As most endurance athletes realize, ultrarunning is an extreme sport, and it doesn’t come without potential risks and complications. A recent study in Physiological Reports reveals that ultra-trail runners face an elevated risk of acute kidney injury, particularly during the first half of a race.
What is acute kidney injury?
Acute kidney injury (AKI), also known as acute renal failure, is a sudden episode of kidney failure or damage that occurs within a few hours or a few days. Following endurance exercise, the kidneys can have trouble removing serum creatinine from the blood (a waste product that the kidneys are supposed to filter). When this happens, the creatinine level in the blood starts to go up, which can lead to AKI.
Due to their long-duration exercise, endurance athletes are particularly susceptible to kidney damage. This vulnerability should be a cause for concern, because AKI can cause reduced urination, digestive disorders, fatigue, vomiting and headaches. In severe forms, it can be fatal.
The study
The study took 55 participants and simulated an ultra-trail race along a course in Clécy, Normandy, France (156 km on hilly terrain, with 6,000 m of elevation gain). During the 156 km, runners ran six loops of 26 km. Refreshment stations were placed at the end of each loop, allowing runners to rehydrate and refuel, as in a typical race. Of the 55 participants, 13 (23.6 per cent) dropped out and did not finish. Three of these runners stopped as a result of musculoskeletal injuries (sprains, fractures, etc.), while the other 10 suffered for various reasons including fatigue, hypothermia, and gastric problems.
To measure participants’ kidney health, researchers used RIFLE (Risk, Injury, Failure, Loss of Kidney Function, and End‐stage Kidney Disease), a score commonly used in hospital intensive care units, to define the severity of AKI. It was found that 88 per cent of the runners presented high RIFLE values during the course’s first two laps, with a peak level of kidney damage occurring around 52 km. In other words, the risk of AKI in ultra-trail runners was highest during the race’s first half.
When runners reached the 78 km mark, RIFLE values fluctuated, with a general decline until racers reached the finish. Researchers suggest this decline results from runners resting at the halfway mark, which gives their kidneys a break. From there, the runners’ RIFLE levels were no longer considered high-risk. Twenty-four hours after the race, it was found that all, except one, of the runners had recovered normal kidney function.
NSAIDs and hydration
Taking nonsteroidal anti‐inflammatory drugs (NSAIDs), such ibuprofen (e.g., Advil), has been found to increase athletes’ risk of AKI; it’s for this reason they are banned at some races, such as the UTMB final.
Taking NSAIDs is common amongst ultra-endurance athletes—one that the study’s researchers caution against. Previous cases of acute renal failure were found in healthy ultra‐endurance athletes who had taken NSAIDs before a race. While the study’s participants did not use NSAIDs, researchers suggest banning their use in trail running to avoid acute renal failure.
Researchers stress the importance of two critical preventive measures to help ultra-trail runners avoid AKI. First, consuming enough water; maintaining proper hydration levels during a race is a direct and effective way to prevent hydration disorders, a significant risk factor for AKI. Second, runners should listen to their bodies and be prepared to abandon an ultra-trail race if necessary.
