Hydrating in the Heat

Hydration is one of the most important components of athletic performance. It is especially important for tennis players since the sport is usually played in hot, humid weather, and without a time limit. Don’t let the intense conditions of Florida take you out of the game; start preparing for the change in weather before you arrive by making these changes:

arrive early—heat acclimatization can take anywhere from one to two weeks, so give yourself the competitive advantage by arriving a few days ahead of play

adopt a fluid plan—thirst lags behind dehydration; keep your hydration “gas tank” topped off at all times by drinking according to a schedule (see next page)

fuel up—increase the amount of sodium in your diet to increase fluid retention

recover—replenish fluid, fuel, and electrolytes immediately following exercise

Unfortunately, a ‘one-size-fits-all’ approach doesn’t work for hydration. Why? Sweat rate and sweat sodium concentration vary dramatically between individuals. It’s these two variables that help determine your unique hydration needs.

What is sweat rate? If you’ve ever heard someone say they’re a “heavy sweater” or a “light sweater,” they’re referring to their sweat rate. This is simply the amount of sweat lost over a period of time. But this variable changes dramatically depending on temperature, location, and intensity of activity. Skiing in January in Colorado is likely to produce a much lower sweat rate than running in August in Florida.

Ready to determine your sweat rate? The easiest way to do so is by weighing yourself before and after exercise, and monitoring how much fluid you drink during exercise. Assuming you do not use the bathroom between weighing in and out, this simple equation will give you your sweat rate:

Sweat Rate = Weight Lost (kg) + Fluid Consumed (L)

Duration of Exercise (h)

What is sweat sodium concentration? Sodium is the main electrolyte lost in sweat and the amount lost varies dramatically from athlete to athlete. Athletes can lose as little as 200 mg/L to as much as 2,000 mg/L of sodium in their sweat. Believe it or not, the average person loses about 920 mg/L!

Are you a salty sweater? If your sweat burns when it enters your eyes, if your skin is coated with a grainy residue after exercise, or if your clothes are streaked with white lines as you’re sweating, it’s likely that you lose a lot of salt in your sweat and may need more salt than a typical sports drink can provide. Speak with a sports dietitian for specific hydration advice.


Improper hydration and electrolyte replenishment can have a negative impact on performance. In fact, as little as a 2% loss of body weight due to dehydration can cause detrimental effects.

An athlete who usually weighs 125 pounds can start experiencing these symptoms after losing as little as 2.5 pounds in a practice; whereas an athlete who usually weighs 200 pounds can begin experiencing symptoms after only a 4.0 pound loss.


Once you know your sweat rate, adopt a fluid plan based on body weight changes and drink according to a schedule to minimize weight loss to less than 2% usual body weight.

When? What? How much?

Before 2-3 hours prior water >16 oz.

15-30 minutes prior 8 oz.

During every 10-20 minutes water + sports drink 6-10 oz.

After for every pound lost water 24 oz.

Do I REALLY need a sports drink? If training for more than 60 minutes—YES! Choose a sports drink to help replenish fluids and electrolytes lost in sweat and provide a quick energy source to sustain performance during intense and longer duration training sessions.

In addition to staying hydrated, use these strategies to keep cool in the heat:

drink cool beverages

• avoid alcohol

wear a hat and light-colored,

• use chilled towels during practice

• limit outdoor activity to the coolest part

take cool showers between activities of the day

Tara Gidus Collingwood, MS, RDN, CSSD, LDN

Trish Kellogg, MS, RDN, LDN tara@dietdiva.net | trish@dietdiva.net

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