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How Much Fluid Should I Drink While Running?

The answer to this question is different for every person because we all have different sweat rates. It also depends on weather conditions and how far or how long you will be running.

If you are running in temperatures under 70 degrees, you should be able to run an hour without having to take in fluids. So most people should be able to run a 5k or 10k race without having to carry or stop for water. However, if you are exceptionally heavy, or the humidity is really high, this may not be true.

Studies have shown that performance starts to be significantly affected after one loses more than 2% of their body weight from fluid loss through sweat. So how do you know how much weight you lose while running? You must do a sweat rate test. It is best to do this in several types of weather conditions and depending on the conditions during your run or race you will know approximately how much to drink.

I recommend a one-hour test. The best and most accurate way to do this is to weigh yourself, in just your running shorts, before you run. It is best to use a scale with 0.1 to 0.2 increments for accuracy. Make sure you drink any fluids and go to the bathroom first. After you have weighed yourself do a one-hour run without drinking anything during the run. Immediately after the run weigh yourself again in just your running shorts. I weigh 162 pounds. At 60 degrees and 50% humidity I will lose about 2 lbs in one hour. Bump the temperature up to 75% and I will lose 3 lbs or more an hour. So how does this translate into how much you should be drinking?

The general rule of thumb is to drink about 16oz for every pound lost. This means at 60 degrees I should take in 32oz of fluids every hour. The best way to do this is to drink about every 15-20 minutes during a run. That means if I were to drink every 15 minutes I would need to consume 8oz of fluids ever 15 minutes. If I drank every 20 minutes I would need to consume about 11oz each 20 minutes.

If you are running an hour or less you should be able to get by without drinking until right after you are done, but any more than an hour and you should definitely be taking in fluids. If you are going to be running longer than an hour you should start your fluid intake in the first 15-20 minutes into your run. Don’t wait until you are thirsty or until you have already run an hour. If you do that you will never be able to catch up during the run as the body can only absorb so much fluid at a time. Though you can increase this absorption rate through practice.

You may find it hard, at first, to drink this much during a long run or race. So you may have to force yourself to drink at first. After a while your body will adapt and it will become more natural.

It is a good idea to always weigh yourself before and after a long run just to be sure you drank enough. Always replace lost fluids after a run as soon as possible.

Russell L Barber