Even mild exercise changes the metabolic processes of the body, causing a need for additional oxygen supply to the muscles and the breakdown of the simple sugar glucose to be used for energy by the working muscles. This change leads to the need for removal of waste products of metabolism by the liver. The kidney in turn filters the blood to remove excess nutrients and waste products for elimination in the urine. This can lead to excess protein in the urine and, occasionally, blood as well.
Exercise Metabolism
Carbohydrates and fats circulating in the blood or stored in muscle in the form of glycogen can be used by the skeletal muscles for energy. According to the Muscular Dystrophy Association, mitochondria inside muscle cells use these nutrients to make the energy molecule adenosine triphosphate also known as ATP. This metabolism results in the release of reactive oxygen species that can damage cell muscle cells.
Hematuria and Proteinuria
Exercise stimulates the production of red blood cells to carry oxygen throughout the body to active muscles. The Mayo Clinic notes that strenuous exercise can lead to blood in the urine, or hematuria, although blood in the urine after mild exercise is more rare. In addition to strenuous exercise, the Mayo Clinic indicates blood in the urine, may be caused by infections, kidney or bladder stones or an enlarged prostate gland for men over the age of 50. Exercise or activity resulting in proteinuria, or protein in the urine, is normal for younger people. However, protein in the urine may also be caused by heart disease, diabetes or kidney disease.
Exercise and Kidney Function
Exercise changes the flow of blood inside the kidneys. According to a rat study published in the June 1, 2010 issue of the "Journal of Sports Science and Medicine", acute exercise increases urinary protein excretion. In the July 18, 2003 issue of "Journal of Applied Physiology," researchers at Akdeniz University in Turkey found that exercise-induced increases in nitric oxide decreases blood flow in the kidney, leading to temporary proteinuria after exercise.
Urine Testing
A urinalysis may be used as a screening test for kidney disease or to determine if prohibited substances have been used by athletes. According to Medline Plus, the normal protein value in a random urine sample is between 0 and 8mg per deciliter, and the normal value of red blood cells is four or fewer RBCs per high-power field. Values higher than these can indicate the use of performance-enhancing drugs. The World Anti-Doping Agency screens athletes' urine for the use of prohibited recombinant human erythropoietin to improve endurance.
References
- Muscular Dystropy Association: Facts About Metabolic Diseases of Muscle
- Mayo Clinic: Hematuria Risk Factors
- "Journal of Sports Science and Medicine"; The Effects of Regular Aerobic Exercise on Renal Functions in Streptozotocin Induced Diabetic Rats; Hatice Kurdak et al; June 2010
- "Journal of Applied Physiology"; Effect of Nitric Oxide on Exercise-induced Proteinuria in Rats; F Gündüz, O Kuru and UK Sentürk; July 18, 2003
- MedlinePlus: Protein - Urine
- World Anti-Doping Agency: The 2011 Prohibited List
