If you having been training for a least a while, you have probably heard that it is important to hydrate during training. What few athletes know, however, is how much fluid is adequate. What I observe is that the majority of athletes either just drink when they are thirsty or take a few sips when the coach tells them they can. But, the thirst mechanism lags behind the body's hydration level. This means by the time an athlete feels thirsty, he/she is already 1% dehydrated. Make it to 2% and you can see real performance detriments. On top of that, thirst is often stunted during activity due to the intensity of the training. Luckily, there is an easy way for every athlete to get an idea of where their fluid needs range.
Sweat rate testing
By using pre- and post-weights, athletes can quickly calculate the amount of fluid their bodies sweat out during exercise. This is because in an acute training session, the only true weight that is lost is water (not muscle or fat). So any change seen on the scale can be completely attributed to water. Here is an example:
Male Athlete Pre-weight: 155
Male Athlete post-weight: 152
Total weight lost: 3 pounds
Every pound lost is equal to 16 ounces of sweat. So, assuming this workout was 1 hour long, this athlete sweat 48 ounces (or 6 cups) of fluid during training. Now, for this athlete, 3 pounds is in fact 2% of his body weight. So, a 3 pound loss during training could have negatively impacted his performance of the training session he just completed. Moving forward, this athlete now knows that for a similar intensity training, he should be drinking at least 3 cups fluid to cover for at least half of his sweat losses, assuring he is no more than 1% dehydrated.
It is important to note that when doing a sweat rate test, athletes cannot go to the bathroom (unless they want to measure the volume of output). If anything is eaten, the weight of the food needs to be added into the equation, as that affects the post-weight. It is a good idea if training sessions last a solid 60 minutes to get good data on the body's sweat amounts.
With a scale and attention to detail, obtaining better knowledge of fluid replacement is just a workout away.
Your Nutrition Coach,