Sean N. Martin
Michael W. Johnson
Hematuria and proteinuria are the most common urinary findings in athletes. It is estimated that between 17% and 22% of marathon runners experience postrace gross or microscopic hematuria (5,14). Similarly, 55% of rowers and football players, 73% of boxers, and 80% of swimmers, lacrosse players, and track athletes experience postexertional hematuria (1,3). Further, 30%-69% of runners develop proteinuria following the completion of a marathon regardless of gender (5,15).
Acute renal failure in athletes is a rare event and is usually associated with volume depletion, rhabdomyolysis, or the nephrotoxic effects of nonsteroidal anti-inflammatory drugs (NSAIDs).
Although the incidence has not been directly studied, studies have demonstrated that sports are responsible for up to 30% of renal trauma in the pediatric population (2). Contusion is the most frequent kidney and bladder injury, whereas laceration and rupture may be life threatening. Athletes in gymnastics, horseback riding, football, ice hockey, rugby, boxing, and soccer have the highest incidence of renal trauma, whereas bicycle riding is the most common sports-related cause of renal injury (8). Overall, individual sports, rather than team sports, account for the majority renal injuries (13).
The male genitalia are often subjected to trauma ranging from testicular contusions to penile frostbite. Bikers are at risk for overuse pudendal nerve injury and straddle injuries.
The prevalence of sexually transmitted diseases (STDs) in athletes is similar to that of the general population, although a study of college athletes showed they tend to be at higher risk for certain lifestyle behaviors. These maladaptive behaviors include less safe sex, greater number of sexual partners, and less contraceptive use when compared with their nonathlete peers (14).
The genitourinary system is comprised of the kidneys, ureters, bladder, urethra, and genital organs and is located in the lower abdomen and pelvis.
The kidneys can be found high in the retroperitoneum bilaterally and are well protected. A malpositioned kidney is prone to injury, while the presence of a solitary kidney places the athlete at especially higher risk. The urinary bladder is located in the anterior pelvis and is rarely acutely injured.
The kidneys receive more blood flow per unit weight than any other organ in the body. Renal blood travels to the glomerulus via the afferent arteriole and exits through the efferent arteriole. With afferent arteriole constriction, a pressure drop occurs within the glomerulus and filtration fraction decreases. With efferent arteriole vasoconstriction, pressure increases within the glomerulus thereby increasing the filtration fraction.
Exercise causes acute changes in a variety of organ systems, as exercising muscle requires a significantly larger proportion of cardiac output. Blood flow is shunted away from the kidney to meet the demands of working muscle. Studies have noted a drop in renal blood flow from 1,000 mL/min to as little as 200 mL/min with exercise, a decrease that is proportional to the intensity of exercise (6,11). Interestingly, there are conflicting data correlating intensity and duration of exercise as independent variables causing hematuria (9,17).
In an attempt to maintain glomerular filtration rate, the efferent arteriole constricts to a greater degree than the afferent arteriole, creating a “pressure head” at the glomerulus. Additionally, the nephron becomes partially hypoxic, causing increased glomerular permeability. These two mechanisms account for the increased urinary erythrocyte concentration.
The increase in filtration fraction is attenuated by improving the runner’s hydration status. Poorly hydrated individuals have a significantly larger decrease in renal blood flow compared with normally hydrated individuals.
With moderate exercise (50% [V with dot above]O2max), renal plasma flow decreases by 30%, whereas with heavy exercise (65% [V with dot above]O2max), renal plasma flow decreases by 75%. These changes are temporary, and renal blood flow typically returns to preexercise levels within 60 minutes of exercise cessation (7).
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