2.5. Nitrogen Balance

The urine samples were stored at 4 °C until analysis after acidification with anhydrous citric acid. The creatinine and urea concentrations in the urine were measured by SRL Medisearch, Inc. (Shinjuku, Tokyo, Japan). Nitrogen excretion was calculated by summing the urinary excretion of urea-bound nitrogen and creatinine-bound nitrogen, which represents >75% of the total nitrogen excretion in athletes [11]. NBAL was estimated as follows: NBAL = E − I, where E represents nitrogen excretion and I represents dietary nitrogen intake, calculated as the intake of protein and amino acids on day 3 divided by a nitrogen-to-protein conversion factor (6.25).