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If you want this jersey, you’ve got to piss blood for it.

Attributed to All Black rugby player Mark Shaw in conversation with his successor Mike Brewer

The kidneys are important but often neglected organs. Exercise can have significant effects on renal function. The most serious renal problem is rhabdomyolysis. Other common renal problems include post-exercise protein/hemoglobinuria, and non-steroidal anti-inflammatory drug (NSAID)–induced renal dysfunction and/or injury. Renal trauma can result from sports-related abdominal injury.

Clinical anatomy and physiology

Ordinarily, the kidneys are paired organs that lie under well-developed flank muscles.1, 2 Kidneys receive high blood flow (approximately 20% of the total cardiac output at rest) and are composed of metabolically active cells. These cells are susceptible to hypoxia, and tolerate this poorly. The tubular arrangement within the kidney uses a countercurrent mechanism to produce hypertonic urine.

The four major functions of kidneys are:

  • to maintain salt and water balance

  • to excrete nitrogen, mainly as urea

  • to produce erythropoeitin and the vitamin D metabolite 1,25-dihydroxycholecalciferol

  • to regulate blood pressure via the renin-angiotensin-aldosterone system.

Normal values for renal function at rest and with exercise are listed in Table 52.1.

Table 52.1

Renal function—normal values

During exercise, physiological changes that have been observed are:

  • increased glomerular permeability

  • increased excretion of red blood cells and protein into the urine

  • renal vasoconstriction, especially of efferent arterioles

  • increased filtration pressure

  • relative stasis of blood in glomerular capillaries.

Collectively, these changes result in a degree of hypoxic damage to the nephron.

In addition to the above, there is also:

  • decreased urine flow, mainly due to antidiuretic hormone (ADH) secretion.

Exercise-related renal impairment

Exercise-related renal impairment usually occurs as a result of dehydration. Exercise results in fluid losses of 1–2 L/hr, particularly in hot conditions. Replacement rarely matches this fluid loss, so a cascade of events may occur as depicted in ...

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