Fluid Replacement Does NOT Lower Body Temperature?

Our research, which for the first time measured internal body temperature continuously during an actual race, revealed no evidence that fluid intake makes runners cooler or improves performance.'

The highest body temperature observed (41.7°C) was recorded from a runner replacing the greatest amount of his sweat losses (73%) and therefore being the least dehydrated of the study sample. (my guess is fitness level had something to do with this).

-sciencedaily.com

This is the first time I've ever seen measurement of body temperature change using a technique other than rectal.

When you think about it, the evaporation of sweat from skin is what actually cools you down during a race, but when your fluid levels get real low...?

...while fluid losses led to an average fall in body mass of 2.3kg (about 3% of body weight), the athletes’ core body temperature averaged only a modest 1˚C above normal resting temperature, while other measures of dehydration, including plasma levels of sodium and urine concentration, stayed within normal ranges. -peak performance

If you read on, note that when fluid loss reaches 5% of your body weight, as in severe dehydration, rectal temperatures do rise.

If You Think You Need Electrolytes- READ THIS!

1.Sweating causes some sodium loss, but because the sodium content of sweat is so low relative to body fluids, your sodium concentration will rise. And it is the concentration that is important, since this controls fluid shifts in the body. It is NOT possible, even for a "salty sweater" like Randy in these scenarios, to LOSE sodium through sweat.

2.Rather, we have demonstrated that the only possibly theoretical way that the sodium level can fall is if Randy drinks too much. If he drinks more than he sweats, then he will really be in a lot of troube. For example, if Randy took Gatorade's earlier advice and drank 40 Oz per hour (1.2 L), then his sodium levels would fall to 125mM

Anybody considering a marathon or beyond should read this interesting post on fluid and electrolyte replacement. Take the time to read through the facinating debate on this subject that follows. The Science of Sport

There are companies out there now (Enlyten, Ultima Replinisher) that market electrolyte replacement as essential for optimal performance, even more so than carbohydrate (which is absurd!)

Fluid Replacement

If I lose a pound of sweat, how much fluid volume do I need to drink to replenish that lost weight? Does water weigh more or less than sweat? Does it make a difference, in terms of volume, if I'm drinking a recovery drink versus water?

A. There is an old saying, "A pint's a pound, the world around." Go to active.com for a more complete explanation.