• Urine specimens were obtained from 47 football players who had passed complete physical examinations and denied renal disease. Each submitted at least one normal specimen together with additional specimens before and after games or strenuous practice.
Each day was scored as to the severity of the required exertions, and this score was found to be roughly proportionate to the frequency of abnormalities in the urine. On no day did every member of the squad submit a completely normal specimen In addition to protein, the more unusual types of formed elements appeared in 27 of the 424 urine specimens examined; these included red blood cell casts in 10, epithelial casts in 7, broad casts in 3, and white blood cell casts in 3. During the study, gross hematuria appeared in one subject. In every instance, the abnormalities disappeared when the daily exercise was made less severe.
These findings explained the spontaneous recovery of an athlete whose history of gross hematuria, which is given in some detail, had raised the suspicion of acute glomerulonephritis.
Gardner KD. "ATHLETIC PSEUDONEPHRITIS"-ALTERATION OF URINE SEDIMENT BY ATHLETIC COMPETITION. JAMA. 1956;161(17):1613-1617. doi:10.1001/jama.1956.02970170009003