While athletes are often aware of the importance of hydration, few have a plan for how they will hydrate based on their individual needs. What I observe is that the majority of athletes either only 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 that by the time an athlete feels thirsty, he/she is already 1% dehydrated. At 2% dehydration, performance can be decreased by as much as 10%. Thirst is also 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 during that training session 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 performing 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.
If an athlete finishes a workout and has lost weight during that workout, that athlete should drink 3 cups of fluid per pound of weight lost during that workout. This is to help the body with the rehydration process. So, in the example above, the athlete lost 3 pounds. That means he should be drinking 9 cups in the 1-2 hours post workout to help with rehydration!
Hopefully, with better knowledge of his sweat rate, he can prevent such large sweat losses in the future.
With a scale and attention to detail, obtaining better knowledge of fluid replacement is just a workout away.
Your Nutrition Coach,