Renal alterations during exercise.

Proteinuria and hematuria are common during exercise. Proteinuria is usually due to glomerular or tubular changes or to an excessive production of protein as in myeloma. Certain clinical conditions can, however, result in a functional or temporary proteinuria, especially during pregnancy, fever, orthostasis, or following physical activity. Sport-related proteinuria following marching, exercise, and stress, was first observed in soldiers after long marching. Prevalence of proteinuria during exercise ranges from 18% up to 100% depending on type of exercise and its intensity. A higher incidence of proteinuria has been observed in some sports requiring great exercise intensity and it is certainly related to muscular work intensity and would decrease after prolonged training. Indeed, exercise-induced proteinuria is strictly related to exercise intensity rather than to exercise duration. Exercise aggravates the proteinuria of various nephropathies and that of renal transplant recipients. The prevalence of hematuria is higher in the athletic than the general population and the main difference is that sport-related hematuria resolves spontaneously after physical exercise while hematuria found in nonathletic population can be chronic. Sport-induced hematuria is influenced by exercise duration and intensity. Among the mechanisms underlying the exercise induced hematuria are increased body temperature, hemolysis, increased production of free radicals, and excessive release of catecholamines. Lactic acidosis, generated during anaerobic conditions, causes the passage of erythrocytes into the urine, through increased glomerular permeability.