Four simple points to remember:
1) It is much easier to recover in an event due to decreased nutrition than decreased hydration – you can recover in 10-15 minutes if your nutrition is off, it would take about 2-5 hours to recover from a dehydration issue. So a race consideration in hot conditions would be to get as much nutrition from a liquid source as possible.
2) Know the signs of dehydration, and remember once you have had a heat issue your body resets its feedback mechanisms. This means your next heat related issue will happen earlier and potentially more dramatically then the time before.
Your body will start to show signs of dehydration and performance will be impaired with a 2% reduction in fluid levels. The graduated signs of dehydration are as follows:
Thirst, Loss of appetite, Lack of sweating/dry skin, Skin flushing, Dark coloured urine, Dry mouth, Fatigue/weakness, Chills/goose bumps, Dizziness
If the dehydration is allowed to continue, when the total fluid loss reaches 5% the following effects of dehydration are normally experienced:
Increased heart rate, Increased respiration, Decreased sweating, Decreased urination, Increased body temperature, Extreme fatigue, Muscle cramps, Headaches, Nausea, Tingling of the limbs
General Fluid loss and replacement levels vary with individuals as do electrolyte levels. However, the following levels have been recorded in longer (i.e. half Ironman distance and longer) events.
3) Average fluid loss during the bike 800ml/hr, average during the run 1025ml/hr
The average replacement is higher on the bike (approx. 850ml/hr) and much lower on the run 625ml/hr. So the note to remember is over hydrate on the bike (with water and other electrolyte/carbohydrate) fluids to make up for the discrepancy on the run.
4) Lastly, if racing in the heat it is a good idea to start your salt replacement 2-4 DAYS early. As a rule, the body will not stockpile electrolytes however it will replenish all levels and make sure you get to the start line topped up (and maybe even a pound or kilo heavier due to water storage – not a bad thing for a long event!)
If you have questions about this topic or any other ideas for coaches corner please contact me at firstname.lastname@example.org