Your kidneys will thank you ….

Posted on 12 January 2019

Doctors involved in multi-stage extreme events continuously highlight the need for good hydration to maintain performance. Due to the repeated nature of the exertion, each athlete must fully understand their body to compensate daily for natural loss of water, salt and electrolytes during each stage.

The importance of hydration for athletes

  • Water makes up approximately 92% of blood with 8% blood plasma proteins, and trace amounts of other materials making up the rest
  • 75% of your muscles are water – dehydration may limit your muscle’s ability to contract – which in turn may affect your strength and speed
  • Water helps transport oxygen and nutrients around your body
  • Water helps regulate body temperature
  • Dehydration may vary from simple thirst, to impeding your performance as an athlete and then possible mental decline. Further dehydration can result in organ damage or admission to hospital
  • Over-hydration is also possible – by replacing water only without balancing this with electrolyte replacement, this may result in the electrolyte levels of the rider being diluted – thus affecting the muscles’ ability to function

How our body copes with dehydration

When considering the blood’s viscosity (or resistance to flow), it is important to remember that dehydration has been shown to increase blood viscosity. This means that the heart must work harder to move it around and that it is also more likely to form clots inside the arteries and veins. In one study, dehydration increased the systolic blood viscosity by over 9%.

“Our bodies however, are amazing machines,” says Dr Darren Green, Mediclinic Race Doctor for the 2019 Absa Cape Epic event. “A system known as renin-angiotensin system regulates blood pressure and fluid balance in our bodies. When our blood volume or sodium levels are low, or blood potassium is high, cells in the kidney release an enzyme called renin. Through a process involving the liver and lungs, renin is converted to angiotensin II, which causes blood vessels to constrict and blood pressure to increase. The release of the hormone aldosterone in the adrenal glands is stimulated, causing the renal tubules to retain sodium and water, while excreting potassium. Together, angiotensin II and aldosterone work to raise blood volume, blood pressure and sodium levels in the blood, while restoring the balance of sodium, potassium, and fluids. The warning for athletes is that if the renin-angiotensin system becomes overactive, it can result in consistently high blood pressure.”

Our advice remains that monitoring your fluid levels can reduce the need for your body to undergo these stressors.

How do I determine my personal sweat loss ratio?

Before exercising, weigh yourself naked. Following an hour of exercise (that resembles the conditions you will be racing in) weigh yourself again. This will represent your sweat loss per hour.

According to Dr Darren Green, “No two athletes are the same when it comes to recommendation for fluids. It pays to understand your own sweat loss and then rehydrate accordingly. Your personal loss may relate to age, genetics, gender as well as your fitness level – which implies that there is no central formula that can be applied to training or race conditions.”

“In recovery, it is important to note that on average, water and other drinks fulfill 80% of our total daily water needs with food making up the other 20% of these requirements,” so keep this in mind when balancing your recovery nutrition.

One final word from Dr Green, “In the absence of sufficient hydration, the use of anti-inflammatories can result in permanent kidney damage. So please be wise in your use of any medication. Our team is at the race hospital and on the route, please make use of our clinical expertise to ensure the best outcome for you.”


Published in Cape Epic

In the interest of our patients, in accordance with SA law and our commitment to expertise, Mediclinic cannot subscribe to the practice of online diagnosis. Please consult a medical professional for specific medical advice. If you have any major concerns, please see your doctor for an assessment. If you have any cause for concern, your GP will be able to direct you to the appropriate specialists.

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