We visited the Glen Canyon Dam at Lake Powell recently and it really caused me to stop and think about the immense power and necessity of water. It destroys landscapes, powers cities, transports goods. All living things, from the tiniest insect to the largest towering tree, require water to survive.

As with most things in life, my mind wandered to the runner’s perspective. I have not always been a stellar example of proper hydration- in fact I’ve probably spent more of my life dehydrated than the opposite, but I notice a huge difference in the way I perform and feel when my body is hydrated. Let’s look at how important proper hydration is for a runner.

How Dehydration Affects Running Performance

Performance takes a negative hit as the body become dehydrated. Sweating reduces blood volume, so less blood returns to the heart. As a result, the amount of blood the heart pumps with each beat decreases and consequently, less oxygen-rich blood reaches working muscles. The rate of aerobic energy production decreases and the runner must run at a slower pace. 

These effects are magnified on a hot day because the body sends more blood to the skin to help remove heat, thus even less blood is pumped to the working muscles. The result is a higher heart rate for a given pace and the inability to maintain the same pace as on a cool day. At the same time, dehydration also reduces the body’s ability to maintain core temperature because less blood is available to be sent to the skin and the sweat rate decreases.

Studies have found that dehydration of two percent of bodyweight leads to about a six percent reduction in running performance. Even a small amount of dehydration causes a decrease in running performance. In addition to the negative effects on running performance during a run, dehydration slows a runner’s ability to recover for tomorrow’s workout.

An Interesting Study

A new study out of the University of North Alabama presented at the American College of Sports Medicine’s annual meeting emphasizes the importance of monitoring hydration levels during a workout.

Researchers gathered 13 distance runners and had them run a 75-minute evening run followed by a 10K time trial the next morning on two separate occasions. They monitored sweat loss, hydration and 10K performance in both instances. The difference between these two evening/morning runs was how much the runners drank. After one of the evening runs, they rehydrated 75 percent of their sweat loss, which is typical of what many runners do. After the other evening run, they rehydrated 150 percent of their sweat loss, which is what the American College of Sports Medicine suggests.

The difference in 10K performance the following morning during both experiments was striking. When runners replenished 150 percent of their sweat loss, their 10K times were on average over a minute faster, which was a three percent improvement over running at the 75 percent hydration state. Put into other terms, that could be the difference between a 4:00 and 3:52 marathon.

The researchers concluded that while 150 percent replacement of sweat loss may be overkill, runners should be replenishing at a rate of slightly over 100 percent to garner performance benefits.

How much should you drink? 

The amount you need to drink to stay well-hydrated depends on the severity of the heat and humidity, how much you tend to sweat, your body size, and how much and how intensely you are training. Your baseline fluid needs are about a half gallon per day. On top of that, you need to add your fluid losses from training and other activities. If you replace a little less fluid than you lose each day, after a few days your running will suffer without obvious reason.

Experts recommend weighing yourself before and after running to determine how much weight you lost and drink enough to bring your weight back up to its pre-run level. Because you do not retain all the fluid you drink, becoming fully hydrated typically requires drinking an amount of fluid equivalent to about 1.5 times the amount of weight that you lost.

Be sure to spread your water consumption throughout the day and don’t try to cram it in just before or after a run. Keep a water bottle handy and filled. This can also help you keep track of how much you are drinking. There are also phone apps available to remind you to drink and monitor quantity. Keeping an eye on your urine color is also helpful. Light yellow, like lemonade, is the goal.

Hydrating during a run or race can be a little more complicated and requires some finesse and practice. All lost fluids don’t need to be replaced during a run, so drinking for thirst is a good bet. Maintaining sodium consumption can aid your body in absorbing the water and can help prevent nausea and cramping.

What should you drink?

Obviously your body needs water to stay hydrated, but sweat also contains sodium, magnesium, and potassium, so those need to be replenished as well. They play a pivotal role in maintaining fluid balance and muscle function. Most Americans don’t consume the recommended 400 mg of magnesium and 4,700 mg of potassium each day. A deficiency in either mineral can amplify the symptoms of dehydration and cause extreme muscle cramps. 

During running, water and carbohydrate replacement drinks are both excellent for maintaining hydration. The advantage of replacement drinks while you run is that they are absorbed as quickly as water, while providing readily usable energy. Many runners choose water for hydration and gels or chews for fuel. Gels often don’t contain enough sodium to maintain proper fluid balance, so it’s a good idea to incorporate sports drinks, electrolyte mix or salt tablets as well.

After running, many other options are available. Some runners choose coconut water because it is a natural electrolyte replacement, containing carbohydrates, magnesium, and potassium. Watered down fruit juice is another option.

Practice healthy hydration habits and see if your running improves!