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10K runners should pre-hydrate with salt in hot weather, new study finds

Runners who took a little sodium with their water pre-race did not run faster, but needed less water during the race, and finished less dehydrated than when they drank only water

A small but significant study slated for publication in the Journal of Human Sport and Exercise shows that 10K runners who pre-hydrate with sodium in warm, humid weather won’t run any faster, but they will stay better hydrated throughout the race than they would by pre-hydrating with plain water. This could benefit performance indirectly, since dehydration can lead to overheating, which can be dangerous.

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The study followed 10 men between 18 and 40 who ran a 10K after pre-hydrating with water only, one hour before the race. One week later they ran another 10K race after pre-hydrating with water plus sodium (12 mg sodium per 5 mL water), as much as they wanted. Their heartrate, blood pressure, body mass, temperature, sweat rate and state of dehydration were all measured before and after the race, and their times compared. On both days, the temperature was 28 C, and relative humidity was high (75 per cent on the first day, 77 per cent on the second day).

There was no significant difference in race times between the two days. But there were significant differences in how much they needed to drink during the race, and in their rates of dehydration after the race. Those who had pre-hydrated with sodium drank less than half as much water during the race as those who pre-hydrated with water only, but they were also more than one-third less dehydrated after the race, and their sweat rates were less.