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Drink, But Not Too Much: Hydration and Hot Weather Running

In the words of Ron Burgundy, “Well, that escalated quickly.” Spring appears to be over and we’ve passed the five days of ideal running weather in upstate New York. Therefore, it is time to think about running in the heat, which means thinking about hydration.

The simple science of hydration

Hydration helps you run better. Your total blood volume decreases when you sweat. As your blood volume reduces, your body loses its ability to transfer heat, and as a result the heart muscle needs to work harder. Your heart also has to work harder to get oxygen to your muscles. You need to take in sufficient liquid to keep your blood volume up, which helps your heart and muscles, improving your athletic performance.


Dehydration can have dire effects on performance. Starting out dehydrated in a 12K race on an 80-degree day, according to a 2010 Runner’s World article, can result in a two-and-a-half minute slower finishing time.


Well-trained runners sometimes “stay ahead of their thirst,” and ignore their need to hydrate. While performance might not immediately suffer, the medical effects can be catastrophic. The best example of this complete crash is Alberto Salazar, who was given last rites at the 1978 Falmouth Road race as dehydration prevented his body from dissipating heat and his temperature reached 107 degrees. Not content with nearly dying once, Salazar again pushed his body to the limits during the “Duel in the Sun” at the 1982 Boston Marathon, when he famously didn’t take any water during the last eight miles and wound up in danger of cardiovascular collapse at the finish, this time with a low body surface temperature of 88 degrees. It cannot be stressed enough: extreme dehydration during exertion can be life threatening.


(The author rethinks his hydration plan)


Going to extremes: Over-hydration

Because Salazar’s brushes with death are legendary, they served to underscore the idea that dehydration needed to be avoided at all costs. However, one can overdo it in the other direction. It is indeed possible to overhydrate.

Ingesting too much liquid can lead to a condition called exertional hyponatremia or EH. This results when blood sodium levels fall due to sweating combined with excessive intake of water, which can further dilute sodium levels in the blood. This leads to nausea, vomiting, extreme fatigue, respiratory distress, dizziness, seizures, and coma.

Unfortunately, all of these symptoms are also indicators of heat stroke, which requires different first aid treatment and medical responses. EH, for example, requires the administering of an IV of hypertonic sodium replacement, a diuretic if hyperhydrated, and an anti-convulsive drug if the afflicted runner is suffering from seizures. Although heat stroke is a serious affliction, the first response is often the administering of fluids while trying to cool the body. Giving a stricken athlete a diuretic sounds counterintuitive and might be one of the last things on a medical volunteer’s mind, yet confusing EH and heat stroke can be fatal. It cannot be stressed enough: drinking too much can be life threatening.

Finding the happy medium: listen to your body

So, how do you figure out how to be adequately hydrated for optimum running performance without spending all your time in the porta-potty line? First, we all have to recognize that we’re not camels – water can’t be banked. One has to match fluid intake with fluid loss.

Figuring out how much fluid you lose during a training run can help to gauge your needs. You have to replace what you lose, no more and no less. One way to do this is to weigh yourself before and after some of your runs. If you have gained weight after a run (and did not make a side trip to Stewart’s for a milkshake), you are drinking too much and need to back off the water bottle. If you notice salt streaks on your face after a run, you have lost a lot of sodium, so you will need to replenish electrolytes with a sports drink, or drink some water in combination with some food that contains sodium. I find this to be a good excuse for salty snacks. Dip some pretzels in peanut butter and you have just created an easy post run recovery food that includes some protein for muscle recovery. Chocolate milk is a popular post-run recovery drink, supplying necessary hydration, some carbohydrates, and some protein. It also tastes good. (Unfortunately, beer, many an adult runner’s standby recovery beverage, is light on protein.) Water, for most purposes, is the ideal hydrator.

If you’re planning a run or race under an hour, be sure to start hydrated. Here, a simple urine test is all that is required. If your urine is clear, you are overhydrated. Straw-colored urine is ideal and if your urine resembles iced tea, you need to drink. Drinking eight to sixteen ounces one to two hours before a run should be plenty. Also, listening to your body is critical. Are you thirsty? Drink some water. Your thirst response is the simplest and best way of determining when to drink.

For runs longer than an hour, carry a water bottle and sip water when needed. Again, drink when you are thirsty. Sipping water when necessary makes for more effective fluid absorption than guzzling. You do not want water sloshing around during a run. This can be the first sign of EH.

What should we drink?

Drink what appeals to you, water or sports drinks to replace sodium and electrolytes after longer or more intense runs. Cold water – really cold water – seems to be the best way to improve performance. In a 2010 study, runners who had an ice slushie ran about ten minutes longer than those given just a cold drink. The icy drink lowered body temperature and perceived effort. The takeaway from this study is to put some ice in your water bottle and consider having an iced smoothie before you race.


Ultimately, then, to make summer running more bearable, hydrate before you run. Listen to your body and accurately assess your hydration level. Carry a water bottle for long runs. And remember: drink, but not too much.

Anybody have any experience with heat stroke or exertional hyponatremia? Have any advice for identifying or avoiding these heat-related ailments?

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