Grediagin, A., & Leklem, J. E. (2001). The effect of a 50-km ultramarathon on plasma urea nitrogen concentration and urinary nitrogen excretion. Medicine and Science in Sports and Exercise, 33(5), Supplement abstract 922.

Ss (M = 9; F = 5) completed two five-day trials. Male Ss consumed a standardized diet of 114 g protein and 3000 kcal, and females 88 g protein and 2500 kcal. On day 4 of the first trial, Ss ran a 50-km ultramarathon. On day 4 of the other trial, Ss were inactive. Plasma urea nitrogen was monitored.

The percent of dietary nitrogen excretion was significantly higher on days 4 and 5 of the ultramarathon trial. This indicates that when exercising moderately or intensely over six hours, the second half of the trial registers a three-fold increase in plasma urea nitrogen excretion.

Implication. When running for longer than three hours, athletes should consume more dietary protein than when performing for less than three hours.

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