Wednesday, March 30, 2011
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).
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.