Operating in extremely hot conditions creates a unique set of medical risks. In the link is the medical outline – for non medics, regarding those risks from the Namibia Ultra Marathon training guide.
Dehydration is the most common heat related illness – in fact, it is thought that dehydration could be the single greatest threat to the health of an athlete. When training regularly and for long distances, fluid intake should be made a priority. You must drink fluids all day – not just during training.
Don’t depend on feeling thirsty to tell you when to drink. Thirst is a late response of the body to fluid depletion. Once you feel thirsty, you are already low on fluids. The best indicator of proper fluid levels is urine output and colour. Ample urine that is light coloured to clear shows that the body has plenty of fluid.
Dark urine means that the body is low on water, and is trying to conserve its supply by hoarding fluid which means that urine becomes more concentrated (thereby darker).
Dehydration can be the cause of feelings of fatigue or exhaustion – at all times watch out for signs of dehydration and take on water regularly through out the day.