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Hydration for the Endurance Runner
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Presented by Coach Bill Strachan

Arizona runners face different challenges than runners from many other parts of the country. We have both high temps and comparatively low humidity.  On a hot day with low humidity it is virtually impossible to drink too much water. The real challenge is balancing the fluid intake and the intensity of the exercise with proper recovery & nutrition.

All endurance athletes need to develop a training, recovery, nutrition and hydration plan. Correct food and fluid intake is essential to a successful exercise routine and much more important than all of the pills and supplements that the experts will try to sell you. 

Arizona athletes need to make adjustments and allowances for our extreme summer conditions!  Exercise early, reduce intensity as needed, eat correctly, drink sufficiently and allow for recovery after each exercise activity.

Remember, the blood carries vital oxygen to power the muscles in physical activity.  In hot weather, the blood diverts this blood flow to the surface of the skin to cool the body’s temperature via the sweating process. Sweating heavily reduces your blood plasma volume. It takes an 8-10% blood plasma volume loss in order for thirst to be triggered. What does that mean? It means that if you wait until you are thirsty to start drinking, it is too late!

Exercise Time/Distances & Fluid Needs

<30 minutes.  (5K)   If properly pre-hydrated you probably don’t need to drink, but it’s OK if you want to. Water alone should be sufficient. .

< 1 hour   (10K) This distance probably won’t exhaust your glycogen and sodium stores, but it is suggested that some sports drink be ingested during the race.

< 2 hours  (7-15 miles) This distance will definitely lower your glycogen stores, but your sodium stores are likely OK. Sports drink is definitely recommended during the activity, and rehydration post-workout is absolutely essential.

< 4 hours  (16 – 30mi)  This distance will deplete glycogen stores and put a big dent in your sodium levels. Sports drink plus supplemental food and sodium should be considered on a case-by-case basis.

4 hours +  (Slow Long Effort – Marathon + Ultras) Rehydration, glycogen and sodium replacement is absolutely essential. You cannot perform at these types of distances on water alone.

Maintaining hydration  


How much should you drink?  To know that, you are going to need to do a little math. Don’t worry… It’s pretty simple. In order to know how much you need to drink per hour, we first need to know how much you sweat per hour.

Step 1- Weigh yourself at the beginning of a 60 minute run. (Convert to ounces. There are 16 ounces in a pound.)           

Step 2- Weigh yourself at the end of your run (convert that to ounces again) and subtract that number from your starting weight.

Step 3- Keep track of how much you drank during your run and add that to the difference of steps 1 and 2

Step 4- Subtract your urine output (You probably won’t pee, but if you do, I will leave it up to your imagination to figure out how much.)

Step 5- The number you end up with is your sweat rate per hour. This is the amount you need to make sure you are drinking every hour during a long run. Keep in mind that this is a starting point. You may need a little more (or a little less) depending on the conditions of the day and the intensity of a given workout.       


Consequences of dehydration

In the context of a 120lb runner, 2% dehydration occurs when you are only 3lbs “light” due to fluid sweat losses.