Good hydration is key to exercise in hot temperatures

July 2, 2012 at 2:02 a.m.

Water, next to oxygen, is the most important substance for human life. It makes up 50 to 60 percent of body weight.

Not only does it provide the medium for most body processes to occur, but also is the main component of sweat, acting as a coolant in stabilizing body temperature.

It is also the major component of blood and helps to transport nutrients to exercising muscles, as well as help carry away waste products such as carbon dioxide and lactic acid.

Balancing fluid intake and loss is essential to performance during training and racing.

The more you exercise outside in hot weather, the more fluids are needed in your daily diet. Avoid "hydrating" with fluids such as caffeinated drinks and alcohol, they actually work to dehydrate you.

Besides the obvious choice of drinking water to hydrate, sports drinks are also a good option. Not only do sports drinks help in maintaining hydration levels, they are also a good source of electrolytes, are absorbed more quickly than water, and supply a source of carbohydrates and fuel.

Replacing electrolytes (sodium, chloride, and potassium) can be crucial in performing optimally and fending off cramping.

Drinks containing a 6 to 8 percent concentration of carbohydrates and small amounts of sodium are absorbed 30 percent faster than water.

However, be aware that drinks with more than 8 percent concentrations of carbohydrates can cause stomach distress.

Pre-exercise and racing fluid consumption

Consuming fluids pre-exercise and during helps to keep body temperature and heart rate lower.

The American College of Sports Medicine recommends drinking approximately 17 ounces of fluid about two hours prior to exercising, or one to two cups (8 to 16 ounces) five to 15 minutes prior to exercising.

Prior to my races, no matter the distance, I consume a full liter of water- making sure to enter the race as well-hydrated as possible.

Fluid intake during competition

Don't wait until you are thirsty to drink, it may be too late.

You can lose up to two quarts of water before getting thirsty. The American College of Sports Medicine suggests consuming six to 12 ounces every 15 to 20 minutes when training and racing.

While racing in hot weather, you may require even more. Unfortunately, you will more than likely lose more fluid per hour than your stomach can absorb in attempt to rehydrate.

The goal should be to replace approximately 80 percent of fluids lost. The more you sweat the more fluids you need to consume.

In addition, the more you sweat; you will need to replace electrolyte losses via sports drinks and/or electrolyte tablets.

The average sweat rate is about 1 to 1 and ½ quarts per hour, and you lose about two pounds of body weight per quart of sweat produced.

To find your own sweat rate, conduct a sweat rate test (see breakout box). You can use a Fuel Belt -a belt that is worn around the waist that holds two to four bottles of six to eight ounces each, or use a handheld water bottle to carry fluids on the run. Never leave home on that bike without a few water bottles in those water cages! I usually tell my clients to take in 20 to 30 ounces of fluid per hour at a minimum.

Fluid intake post-run

Start rehydrating immediately after exercise, consuming 16 ounces for every 30 minutes of exercise performed, and taking in 16 to 24 ounces for each pound of body weight lost over a two to three hour window post-exercise.

Another key aspect of rehydration is salt intake, as it works to retain fluids. Consuming salty foods post workout will aid in this, as well as consuming a sports drink.

The hot temperatures of summer in South Texas can not only contribute to massive fluid losses during training, but also negatively impact training times, heart rate and racing performance.

Give yourself a break in hotter temperatures with allowances for slower paces and reaching higher heart rates during workouts.

If you find yourself struggling, limit mileage and intensity in workouts, or even hit the treadmill or an indoor cycling session when needed. Most importantly- drink, drink, and drink! Maintaining hydration levels is a crucial component in how you train and perform in hot temperatures.

Missy Janzow received her B.S. in Dietetics from Southeast Missouri State University and owns Fit4U, a personalized coaching and nutrition business that serves to train the novice or seasoned triathlete or runner. You can reach her with your questions at



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