NAIL­ING YOUR FLUID IN­TAKE

UN­DER­STAND­ING DE­HY­DRA­TION

Triathlon Magazine Canada - - FEATURES - BY DOUG SCOTT

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

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