Finally we will have a Saturday that is warm-ish! We are almost to race day but still have one long run left and two shorter “long” runs. I thought this week would be a good one to talk about hydration and how much you should be consuming while you run. The bottom line is that you will have to drink during your 6.55 or 13.1 mile journey, but figuring out how much to drink can be tricky. Like everything else you should be practicing what you will drink on race day. You want to get your system used to drinking on the run, especially when drinking sports drink so your tummy is used to dealing with it. During the race hit the “water” stops and grab the sports drink for the carbohydrates and also the electrolytes. Your body really likes balance. It wants and needs water but it also needs the other stuff that comes out when you sweat, which are electrolytes (mostly salt NaCl). The question of how much to drink and what exactly to drink has been going round and round in the running community for several years. Since I cannot do this topic justice I’ve asked Professor Steven Devor at Ohio State Exercise Physiology to help. Below is a great discussion from Professor Devor about hydrating the proper way, which is to be very specific to EACH one of YOU. Hydration is not a one size fits all thing and he gives a really easy way to figure out how much you need to put in to keep up with what is going out when you run. Thanks so much to Dr. Devor for this awesome message about hydration. And this weekend might be a great one to do the sweat rate test at the bottom of this message!
The following was contributed by Dr. Steven T. Devor – Director of Performance Physiology for MIT and OhioHealth, and Associate Professor of Exercise Physiology, Department of Human Sciences, and Department of Physiology and Cell Biology, The Ohio State University
Can you Drink Too Much? In Short – Yes
If you want to be successful and complete longer training sessions and races you must avoid or delay dehydration caused by fluid losses from the body. Fluids are primarily lost through sweating, breathing and using the toilet. Years ago the advice was “drink, drink, drink,” and we assumed there was no downside to consuming as much fluid as possible. Unfortunately, consuming large amounts of water without electrolytes can lead to a condition called hyponatremia. Hyponatremia, also known as low sodium concentration or water intoxication, occurs due to prolonged sweating coupled with the dilution of extracellular sodium caused by consuming large amounts of fluid with low or no sodium.
Balance is Key
Sodium, chloride and potassium are electrolytes, and these electrolytes remain dissolved in the body fluids as electrically charged particles called ions. Electrolytes help to modulate fluid exchanges between the different body fluid compartments and promote the exchange of nutrients and waste products between cells and the external fluid environment. There is actually an electrical gradient across cell membranes. The difference in the electrical balance between the interior and exterior of cells facilitates nerve-impulse transmission, stimulation and action of skeletal muscles during running and other activities, and proper gland functioning. If you consume too much water and not enough electrolytes, your body pulls electrolytes from its cells in order to create the right balance for absorption. If you consume too many electrolytes and not enough fluid, your body pulls fluids from within to create the right balance for absorption. The bottom line is your body likes balance. Keeping your body in electrolyte and water balance, or very close to balanced, is part of the challenge as an endurance athlete.
The easiest way to measure your sweat rate is to weigh yourself without clothes on before you do a one hour exercise session. After the hour session, return home, strip down, wipe of any excess sweat from your skin, and weigh yourself again. Assuming you did not use the toilet or consume any fluids during exercise, your weight loss is your sweat rate. For each kilogram of lost weight, you lost one liter of fluid. To convert it to pounds, for each pound lost, you lost 15.4 oz. of fluid. If you drink any fluids or used the rest room between the two weight samples, you will need to include both of these estimated weights in your calculations. Add fluid consumed to the amount of weight lost. Subtract estimated bodily void weight from the total weight lost. I would be sure to record the heat and humidity conditions in your sweat test. Repeat the test in cool and hot conditions. If you are a triathlete, repeat the test for swimming, running and cycling because sweat rates will vary for each sport and vary with environmental conditions.
Through the years I have been able to come up with the following guidelines based on weight and different environmental temperatures. They are only guidelines, so it would still still be best to do the individual tests in a lab. None the less, I believe these are good averages.
Weight 100 pounds
Fluid Ounces Per Mile Depending On The Temperature: 50°F: 3.0 60°F: 3.2 70°F: 3.3 80°F: 3.6 90°F: 4.1 100°F: 4.7
Weight 120 pounds
Fluid Ounces Per Mile Depending On The Temperature: 50°F: 3.6 60°F: 3.8 70°F: 4.0 80°F: 4.3 90°F: 4.9 100°F: 5.6
Weight 140 pounds
Fluid Ounces Per Mile Depending On The Temperature: 50°F: 4.2 60°F: 4.4 70°F: 4.6 80°F: 5.0 90°F: 5.7 100°F: 6.5
Weight 160 pounds
Fluid Ounces Per Mile Depending On The Temperature: 50°F: 4.8 60°F: 5.0 70°F: 5.3 80°F: 5.8 90°F: 6.5 100°F: 7.4
Weight 180 pounds
Fluid Ounces Per Mile Depending On The Temperature: 50°F: 5.4 60°F: 5.7 70°F: 5.9 80°F: 6.5 90°F: 7.3 100°F: 8.4
Weight 200 pounds
Fluid Ounces Per Mile Depending On The Temperature: 50°F: 6.0 60°F: 6.3 70°F: 6.6 80°F: 7.2 90°F: 8.1 100°F: 9.3
Weight 220 pounds
Fluid Ounces Per Mile Depending On The Temperature: 50°F: 6.6 60°F: 6.9 70°F: 7.3 80°F: 7.9 90°F: 8.9 100°F: 10.2
Weight 240 pounds
Fluid Ounces Per Mile Depending On The Temperature: 50°F: 7.2 60°F: 7.6 70°F: 7.9 80°F: 8.6 90°F: 9.7 100°F: 11.2W