By JOHN BOBALIK
John Bobalik is an exercise physiologist and coordinator of the Purdue University Calumet Fitness Center, a comprehensive exercise and workout facility for students, faculty, staff and community members. It also serves as a laboratory setting for fitness management students.
Q. After perspiring during an ambitious workout, how can one know how much fluid should be replaced to restore normal fluid levels?
A. How much one perspires and the amount of fluid one needs to replenish lost fluid can be calculated from one’s pre-exercise scale weight, post exercise scale weight and how much fluid was consumed during the workout. That is according to Registered Dietitians (RD) and Board Certified Specialist in Sports Dietetics (CSSD) Nanna L. Meyer, Melinda M. Manore and Jacqueline Berning, in their article, “Fueling For Fitness: Food and Fluid Recommendations For Before, During and After Exercise.” The article was published in the May/June edition of The American College of Sports Medicine’s Health and Fitness Journal.
For example, Joe Fitness steps on the scale before a 60-minute run and weighs 152 pounds. He returns to the scale immediately following his run and notes that his post-workout weight is down to 150 pounds. During his 60-minute run, he consumed 10 ounces of water to quench his thirst.
A rule of thumb regarding fluid loss is that for every 1 pound of body weight lost, one should drink 16 ounces of fluid to re-gain the weight. Given Joe’s 2-pound workout loss, he should drink 32 ounces.
Given also that Joe drank 10 ounces of water during his run, all told he perspired some 42 ounces of fluid during and immediately following his run. Joe’s rate of perspiration for 60 minutes of exercise is calculated by adding the 32 ounces he lost via perspiration and the 10 ounces he consumed during his run, but also lost through perspiration, generating an overall fluid loss of 42 ounces.
In their article, the aforementioned authors recommend that one should drink 1.5 times more fluid than what was lost to achieve optimal rehydration. Given Joe’s statistics, (1.5 X 42 ounces), he would need to drink 63 ounces periodically throughout the day following his run to insure that fluid levels and body weight return to normal.
If Joe puts back only half the fluid he sweated out from his workout, he’ll start the next morning’s exercise session in a semi-dehydrated state, which means duplicating the same effort for his 60-minute run will be a little more difficult. Additionally, getting into an exercise cycle of sweating out more fluid than one replenishes is a prescription for muscle cramps, dehydration, heat exhaustion and/or heat stroke.
1. Nanna L. Meyer, Ph.D.,R.D., CSSD, Melinda M. Manore, Ph.D., R.D., CSSD, FACSM; and Jacqueline Berning, Ph.D., R.D., CSSD. Fueling For Fitness: Food And Fluid Recommendations For Before, During And After Exercise. ACSM Health & Fitness Journal. May/June 2012.
Filed under Fit Tip.