Tracey knows that proteinuria (protein in the urine) after intense exercise is physiological (normal). However, protein is typically not present in urine. Why is that?

Normally, protein should not be found in the urine. A person who has protein in the urine is said to have proteinuria.

Explanation

Strenuous exercise increases glomerular filtration of low-molecular-weight proteins (β2-microglobulin), which overwhelm the reabsorbing capacity of the tubular apparatus, causing temporary dysfunction and tubular proteinuria. Exercise-induced proteinuria is generally benign and a function of the intensity—rather than the duration—of exercise.1 It occurs most often among athletes participating in such sports as running, swimming, rowing, football, or boxing.2 It’s also transient—lasting 24 to 48 hours.1 Recognizing exercise-induced proteinuria is fairly straightforward—once you know what to look for.