The doctors told me I would never run again, [but] I’m back running. They told me I would be on dialysis for the rest of my life, but I’m not. I had a kidney transplant, it was successful and I’m back doing what I love. So, if you just stay positive and stay focused on something you really want to achieve, you will do amazing things.
Aries Merritt, 110-metre hurdles world record holder
The kidneys are important but often neglected organs. Exercise can have significant effects on renal function. The most serious renal problem associated with exercise is rhabdomyolysis. Other common renal problems include post-exercise protein/haemoglobinuria and non-steroidal anti-inflammatory drug (NSAID)–induced renal dysfunction. Renal trauma may also be the result of a sports-related abdominal injury or trauma. There have been some well-documented cases of renal disease in athletes at the very top of their professions, including Jonah Lomu, the New Zealand rugby union star, and Aries Merritt, the US 2012 Olympic gold medallist in the 110-metre hurdles. Their stories are considered in case studies later in this chapter.
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 13.1.
Table 13.1Renal function—normal values ||Download (.pdf) Table 13.1 Renal function—normal values
| ||At rest ||During exercise |
|Renal blood flow mL/min ||1200 ||300 |
|Glomerular filtration rate (GFR) mL/min ||120 ||60 |
|Concentrating ability: |
Urine osmolality 100–1200 mOsmol/kg water
Serum osmolality 280–295 mOsmol/kg water
Daily urine volume 400–4000 mL
Obligatory water loss 840 mL*
During exercise, physiological changes that have been observed are: