‘DE­HY­DRA­TION WON’T RE­SULT IN SPON­TA­NEOUS COM­BUS­TION’

Runner's World (UK) - - HUMAN RACE - BY SAM MUR­PHY Sam Mur­phy tweets @ Sam­mur­phyruns

I’m just back from a two-hour run on Span­ish soil. It was one of those fol­low-your-nose runs – you’re not en­tirely sure where you’re head­ing but you need to get the miles in. It was warm in the spring sun­shine, and I ran out of wa­ter be­fore I’d even reached dou­ble fig­ures in mileage. None­the­less, I con­tin­ued; the sen­sa­tion of thirst was un­com­fort­able but it didn’t re­ally af­fect my run­ning – my last mile was my fastest.

A few years ago, it would have been a very dif­fer­ent story. I can pic­ture my­self, red-faced and parched by grow­ing panic, plead­ing ‘agua, agua’ at ran­dom front doors and shop coun­ters, fear­ing a dra­matic col­lapse at any mo­ment.

Since ‘drink to thirst’ be­came the pre­ferred maxim for run­ners, I’ve de­vel­oped a much more re­laxed at­ti­tude to hy­dra­tion. On shorter runs, I mostly don’t bother and if I for­get, or run out, it doesn’t worry me.

This has come as a re­lief to my run­ner hus­band, who tried for years to prise from my hand the bot­tle that I stub­bornly car­ried in ev­ery run or race. The fact that I got a PB the first time I raced a 10K with­out wa­ter on board helped me come around to his way of think­ing.

There’s also re­as­sur­ing ev­i­dence from the world of elite run­ning that los­ing two per cent – or more – of your body weight through de­hy­dra­tion won’t re­sult in spon­ta­neous com­bus­tion and, in fact, may not ham­per your per­for­mance at all. Haile Ge­brse­lassie was re­port­edly more than nine per cent de­hy­drated when he set the marathon world record at Ber­lin in 2008, while a 2011 study of the nu­tri­tion and hy­dra­tion prac­tices of Ethiopian elites found that they drank no fluid ei­ther be­fore or dur­ing their runs.

For many run­ners, the mere thought of leav­ing home with­out a bot­tle leaves them dry-mouthed. Thirst – and its sa­ti­a­tion – ful­fils a deep psy­cho­log­i­cal need as much as it does a phys­i­cal one and it can some­times be dif­fi­cult to dis­tin­guish be­tween the two.

I be­lieve there’s also a sub­tle dif­fer­ence be­tween ‘ad li­bi­tum,’ the term used by sci­en­tists in hy­dra­tion stud­ies, and its com­mon in­ter­pre­ta­tion, ‘drink to thirst’. Ad li­bi­tum lit­er­ally trans­lates as ‘at your plea­sure’ – an in­vi­ta­tion to drink when you de­sire it rather than when you feel a need for it. In one in­stance, you’re quench­ing the mind, in the other, the body.

A Greek study found that when pre­vi­ously de­hy­drated ath­letes were given just 100ml of wa­ter dur­ing a sub­se­quent 20-minute time trial they out­per­formed those who re­ceived no wa­ter. Given the lim­ited hy­dra­tion value of such a small vol­ume of wa­ter, the re­searchers sug­gest that the sen­sa­tion of swal­low­ing it must have been the rel­e­vant fac­tor in the su­pe­rior per­for­mance.

In an­other re­cent study, run­ners who drank ad li­bi­tum fared just as well in a 20km race as run­ners who re­ceived a vol­ume of fluid based on their own phys­i­o­log­i­cally de­ter­mined re­quire­ment, de­spite drink­ing half as much.

You could use this as a ba­sis to ar­gue it doesn’t mat­ter how much or how lit­tle you drink on the run (with the ex­cep­tion of very long races or ex­treme heat). But one as­pect of hy­dra­tion that will af­fect your race times is hav­ing to stop for the loo. Many a run­ner has for­feited a PB, or at least added min­utes to their race time, thanks to a midrace pit stop, the re­sult, in al­most ev­ery case, of over-hy­drat­ing be­fore or dur­ing a run. One of my most en­dur­ing race mem­o­ries is of be­ing over­taken by a fit-look­ing guy wear­ing com­pres­sion socks and car­ry­ing a Camel­bak. ‘That’s a bit un­nec­es­sary for a half marathon,’ I thought. A cou­ple of miles later I passed him as he queued out­side a por­ta­ble toi­let. Now that must have been hard to swal­low.

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