NAILING YOUR FLUID INTAKE
Last summer, after I completed a half iron distance race, I wasn’t feeling well so I went off to the medical tent. The nurses gave me a couple of bags of saline while I lay shivering and throwing up. As I was thinking ‘this really sucks,’ I decided that I should learn about dehydration and develop a plan to avoid it in future races.
Basically, we become dehydrated when the amount of sweat we produce exceeds the amount of liquids we consume. Our athletic performance becomes compromised once we have dehydration losses of just one to two per cent of our body weight. For an 80-kg man, this could be less than one kg. So the answer to the question of how much do you need to drink is quite simple: enough to replace the amount you lose sweating. But, since it’s hard to track that in competition, rehydration becomes more complicated. Our sweat rate depends on such things as our race intensity, how well we are acclimatized to the environmental conditions, the ambient temperature and humidity, what clothing we are wearing, whether we were fully hydrated to start and, of course, individual differences. Average sweat rates range from 0.5 litres per hour to 2.5 litres per hour. This is too wide a range of values to base a race hydration strategy on, so developing a personal plan is imperative.
And the answer is not to drink as much as you can. Over-hydrating can lead to something called Exertional Hyponatremia (EH), which is low blood sodium and, in its most minor cases, causes nausea, but in the most extreme can lead to seizures, comas and even death. EH is generally the result of drinking excessive amounts of water, which dilutes blood sodium levels. EH also tends to affect those of us who are “back of the packers,” who are on the course longer and have the opportunity to drink more fluids. Females, and those with a low body weight, are also at more of a risk for EH. Consumption of non-steroidal anti-inf lammatories (NSAID’S) can also increase the incidence of EH because they may interfere with a salt-retaining hormone in the kidneys.
The first step to determining a hydration plan is to calculate your individual sweat rate. This is done during an intensive workout by using the formula of sweat rate = (body weight pre-run – body weight post-run + weight of fluid intake – weight of urine excreted), all divided by exercise time. To be accurate, weights should be taken naked and sweat towelled off. To make the calculations simpler, going to the washroom should be avoided and only premeasured fluids should be consumed. This exercise should also be done under the different environmental conditions expected over the course of the season. For the calculations, assume the weight of both drink and urine is one litre and weighs one kg. So, as an example, if an athlete weighs 74.3 kg at the start of an hour-long workout and weighs 72.9, at the end and we assume he drinks one litre of water and does not urinate during the exercise period, then the amount of fluids he needs to consume is: (74.3-73.9+1)kg/1 hour=1.4 litres per hour.
It’s critical to start a triathlon fully hydrated. And this doesn’t just mean to top up on race day. Athletes need to drink water throughout the day, every day. One article I read said to drink a minimum of one half your body weight in ounces per day. So a 140-pound (63.5-kg) athlete would need 70 ounces, which is just over two litres. This is only to replace water normally lost throughout the day. More fluids must be consumed to replace those lost while working out. Urine colour is a good way to