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Introduction

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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

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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.

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Clinical anatomy and physiology

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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.

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The four major functions of kidneys are:

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  • 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.

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

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Table Graphic Jump Location
Table 52.1

Renal function—normal values

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During exercise, physiological changes that have been observed are:

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  • 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.

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

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In addition to the above, there is also:

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

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Exercise-related renal impairment

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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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