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Hydration: Obey Your Thirst

  • By Matt Fitzgerald
  • Published January 14, 2013

If you’ve been a triathlete longer than a week, you’ve probably been advised at least once–perhaps dozens of times–to consume enough sports drink during races to completely offset weight loss from sweating and to provide 60 grammes of carbohydrate per hour. The rationale behind these recommendations is that full rehydration elevates performance by aiding temperature regulation and reducing cardiac strain, while absorbing carbs at the highest rate possible helps keep muscles topped off with precious glycogen.

Lately, however, these longstanding guidelines have been challenged by studies indicating that, during running at least, such high rates of fuelling can cause gastro-intestinal discomfort and offer no performance benefit compared to just drinking by thirst. A new study (conducted by Dr. Ian Rollo and colleagues at England’s Loughborough University and published in the International Journal of Sport Nutrition and Exercise Metabolism) provides strong support for an at-will drinking strategy during short-duration endurance exercise.

Nine experienced recreational runners participated in the experiment (see above). Each of them completed a 16K road race on three separate occasions, drinking nothing during one race, drinking a carbohydrate-electrolyte sports drink by thirst during another race (which came to an average of 300ml per hour), and drinking at a prescribed rate aimed to provide the recommended 60 grammes of carbs per hour in the remaining race (which came to 1014ml per hour).

In addition to timing the three races, Rollo’s team took measurements of dehydration, core body temperature and gastrointestinal distress. Performance in the no-drink- ing and prescribed-drinking trials was almost identical. But the runners covered the 16K course almost a minute faster on average when allowed to drink according to their thirst.

Rollo says that further re- search is needed to determine why the runners performed better with intuitive drinking despite becoming significantly more dehydrated and taking in 70 per cent less carbohydrate compared to the prescribed-drinking trial. One possible explanation is suggested by the runners’ subjective ratings of gastro-intestinal discomfort, which were significantly higher throughout the second half of the 16K race in which they were prescribed a heavy dose of sports drink.

It’s important to bear in mind that this study involved a race of relatively short duration and subjects who were mostly unaccustomed to drinking during exercise. The one subject who did routinely use a sports drink in train- ing–who happened to be a triathlete–was also the only subject to record his best time in the prescribed-drinking trial. Thus, the authors of this particular study recommend that athletes practice ingest- ing carbs and fluid in training sessions lasting longer than one hour to optimise performance come race day

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