Hydrating in the Suumer Heat

Hydrating in the Summer Heat
Julie Bishop, M.D
July 2004
The hot, humid, sweltering summer months are finally upon us and for different runners the season has different meanings. After the long, dark winter months, there is something decadent about being able to go out for a run as late as 8pm and then firing up the barbeque grill upon your return. If you have chosen a fall marathon, your training is just getting underway, or if you enjoy racing shorter distances, you are in the prime of the season, with a race every weekend. Regardless of the season's meaning to you, one thing is for certain, it is hot, darn hot. Even as you go out for a 9 AM training run, it already feels like you're melting! You only have one bottle of water and there is none available on the trail is this really enough? Should you drink before you go? How much and what, should you drink when you are running? These are important questions to answer before you head out into the blistering summer heat.

There have been a lot of misconceptions regarding hydration guidelines over the years. It was once thought you should drink as much as possible during your long runs and marathons, but recent studies have warned against this. In May, 2003, the USA Track & Field issued new hydration recommendations that urge runners to hydrate based on individual needs, rather than just drinking as much as they can. Pounding down too much water can actually dilute the electrolytes in your blood, which can lead to serious health complications. The condition that causes these complications is called hyponatremia which means low blood levels of sodium. In fact, at the 2002 Boston Marathon, a postrace blood study revealed 13% of the runners studied experienced low blood sodium! But, there is always a catch; all runners need to understand there are risks associated not only with low blood sodium but also with dehydration. The goal is to understand proper hydration and find a balance. A long run in the summer heat and humidity does lead to more fluid loss through sweat than a cool fall marathon. Runners who drink continuously during a 4 hour run in 50s weather are more at risk for hyponatremia than those racing a half-marathon in August. Thus, the runner needs to take that into account when calculating fluid needs. So what is a hot, thirsty runner to do??

Currently, the basic guidelines recommend 8oz of fluid ~1 cup/20 min. Over a one hour period, you should aim for 400-800ml, and not exceed 800ml/hr. The higher rates are for the larger, more muscular runners, faster running, and conditions of increased heat and humidity. If you are running late in the day, drink throughout the day and then try to drink 16oz of fluid 1 hour before the run. Follow the fluid recommendations during your run and don(1)t drink more than you sweat. Realize you want to avoid over- hydration (and thus hyponatremia), but you need to replenish your fluid loss, especially in the heat. Try to eat salty foods before the run/race, and if you are out for a long run and sweating excessively, bring along a small salt packet and take this in the last half of the run.

Drink when thirsty, but don't gulp down the fluids just because they are offered. The heat can certainly throw you off in deciding your fluid intake, so if you are unsure there are a few things you can do. First, monitor the color of your urine. If you are well hydrated, your urine will be clear and light yellow. Next, weigh yourself before and after your runs. For each pound lost you need 1 pint of replacement fluid and then take that into account on your next run during similar weather conditions. Finally, you can actually calculate your rate of sweat loss before your next long run or marathon by using the USATF Self-Testing Program for Optimal Hydration, as described on www.usatf.org. The final question many ask is what should you drink? For runs that last less than one hour, even in the heat, water is generally the recommended fluid replacement. Water is a great hydrator, but it has no calories or electrolytes. Refueling is important for runs >1hr, as well as for excessive sweating on the hot days where you loose a lot of electrolytes in sweat. Sports drinks are an excellent way to hydrate and refuel. However, you should aim for a drink that does not contain more than 10% carbohydrate, with 4-8% being optimal. Gatorade, for example, contains 6% (14 gms) carbohydrate per cup and allows maximal fluid absorption. Carbohydrate concentrations higher than 10% actually slow fluid absorption.

So, enjoy the lazy, hazy, crazy days of summer. Run long and far or fast and short, but stay properly hydrated and run healthy!!