Beat the Heat: Proper Hydration for Summer Athletics

by guest blogger
Michael Padden, LMT, PTA

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You’ve heard us say this a million times: “Be sure to drink plenty of water.” Summer is a critical time for this simple advice. Too many weekend warriors and seasoned athletes alike fail to maintain proper hydration during the summer months, leading to heat -related complications like heat cramps and even heat stroke in extreme cases. Exercising in the heat is a double whammy for your body’s ability to maintain a safe temperature. Rigorous exercise generates a lot of heat, which must be dissipated somehow. The main method the body uses to remove this excess heat is through sweat, especially in hot weather. If the body is unable to regulate its temperature effectively or when the balance of hydration and electrolytes is disturbed, exercise performance is impaired and if unchecked, can result in serious health risks.

Having a refillable water bottle can be a great way to promote better hydration and save money on the cost of buying bottled water.

It’s important to note that many factors influence body temperature during exercise: individual metabolism, body weight, genetics, clothing worn, environmental conditions and acclimatization to those conditions. The body regulates its temperature during exercise in warm environments chiefly through perspiration and evaporation (aka sweat). This means the body will be losing more water during exercise in the heat than it would doing the same activity indoors or on a cool day. Perspiration is made up of both water and electrolytes and as such, it is important to be sure that rehydration includes replacing those lost electrolytes during intense exercise. Because there are so many factors that go into the rate of fluid loss from exercise, it is difficult to give an exact recommendation for fluid intake. Across a variety of athletic activities, it is typical to see fluid loss rates between 1 - 4.25 pints per hour of activity.  That's up to a half gallon of fluid loss!

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It can be difficult to sufficiently replace the water loss from an activity during the activity or immediately after and as such it is particularly important for athletes who perform prolonged endurance activities or multiple intense activities throughout the day to monitor their hydration. Deficits in hydration from one activity can carry over and be further compromised by subsequent activities if steps are not taken to replace the lost fluids and electrolytes. The more dehydrated you become the higher the strain on the body and the greater the impact on exercise performance.

Image from the classic movie "Airplane!"

Recommendations for ensuring proper hydration for exercise include prehydration, drinking during exercise, and rehydration. To safely and effectively prehydrate, it is recommended that you slowly drink 0.075 - 0.1 oz per pound of body weight approximately 4 hours before activity. (that's about a cup of water per 100lbs.) Then, if 2 hours before activity, either you have not urinated or your urine is dark in color, drink another 0.05-0.075 oz per pound of body weight. (That's about another 5-7.5 ounces per 100lbs)  This recommendation ensures that prehydration does not lead to over hydration, which can also have negative effect on exercise performance.
Drinking during activity can be the most vital for long duration exercise but exact recommendations are difficult due to the wide variability in water loss rates. It is recommended that you assess your own needs carefully, adjusting for your activity and the conditions. As a reference point though, typical marathon runners would likely need to consume approximately 16 - 32 oz per hour to replace their water losses on a warm day.

Replacing salts, AKA, electrolytes can be just as important for proper hydration.

Remember to replace not only the water but also the electrolytes lost during activity, either by consuming a salty snack or by drinking a sports drink, which contains sufficient electrolytes, during your activity. If you were able to sufficiently maintain hydration throughout exercise, then normal meals and beverages may be enough to rehydrate following activity, but if you have built up a deficit, then rehydration will need to be proportionately more aggressive. It is important during this phase to ensure that sodium levels return to normal or the body will not be able to absorb the water it needs to replace the fluid losses. The best way to measure how much fluid needs to be replaced after activity is to weigh yourself before and again after the activity and then drink approximately 23 oz per pound lost, but do so gradually so as to maximize absorption.

References:
Michael N. Sawka, FACSM (chair); Louise M. Burke, FACSM, E. Randy Eichner,
FACSM, Ronald J. Maughan, FACSM, Scott J. Montain, FACSM, Nina S. Stachenfeld,
FACSM.
Exercise and Fluid Replacement, Medicine & Science in Sports & Exercise: February
2007 - Volume 39 - Issue 2 - p 377-390.
doi: 10.1249/mss.0b013e31802ca597