Staying Hydrated & Avoiding Heat Illness this Summer






Dr. Kristal Nelson PT
Board Certified Sports PT

You know the feeling. Your legs are heavy, your energy is zapped and you feel like you can’t get enough air. It’s our summer time ritual of transitioning from the cool/dry temps of spring to the dog days of summer. Avoiding heat illness at tournaments like NC State Tennis Championships can be very tricky, so with that in mind let me address acclimatization, hydration, muscle cramping, and rehydration as well as risk factors, symptoms, and response to heat illness.

Getting Acclimated

No matter how many years you’ve been living in the heat, your body has to re-acclimate each year. So, when we have a sudden change in temperature, everyone suffers. Here’s how your body adjusts:

  1. Your body begins to sweat more efficiently producing more sweat, sweating at a lower temperature, has lower salt concentration, and (with the lower salt) cools the skin quicker
  2. Metabolism decreases a little by putting more fluid into your blood reducing heart rate to reduce the body’s workload.

Your body can’t accomplish this in a split second. In fact, it takes a day or so before it even starts trying. It takes TWO WEEKS and will only accomplish the goal if it is exposed to a minimum of two hours of heat every day for two weeks. Start now!

To get acclimated you need to take it easy the first few days of exposure when possible. Drive without AC, have lunch outside – even in the shade, do light yardwork. Try not to spend all day in the air conditioning. Playing tennis in the heat is a great idea but take frequent hydration/shade breaks and wear loose clothing in the first few days. You lose two thirds of your heat from the waist so wear loose clothing. Drink plenty of fluids so you can get the sweat process working. Finally, staying in shape helps since your body doesn’t have to work as hard during activity. We all know that fat is an insulator so that works against us when trying to cool down.

Quickly, the limits of heat acclimation are those taking certain medications (including antihistamines), those with chronic disease, or those in their 60’s and older. You need to take special care getting acclimated. See the chart for more player controlled risk factors for heat illness.

2% Dehydration = 10% Performance Deficit

10% is certainly the difference between winning and losing


The most critical risk factor for heat illness is dehydration because when dehydrated the body loses the ability to cool itself.

Drinking water during play, obviously critical, is only part of the answer. For best performance levels, you need to replace your carbs and electrolytes (sodium, potassium). Carbs are required to keep your energy levels up during play so you don’t BONK. Sodium specifically helps regulate how much water a cell can hold. If you drink water alone, your cells take on too much water – in serious cases you are essentially drowning your cells which is called hyponeutremia (see below). This is dangerous.

Finally, your hydration level on any given day is highly dependent on what you did the day before. This is why tournaments like the State Championships are tricky as you are playing in the heat day after day or playing multiple matches in a day. Rehydration is KEY!

Which Drink is Best?

Gatorade gives you a perfect balance of fluid, carbs (energy), and electrolytes. Personally, Gatorade gives me nausea so I prefer something natural with only fruit sugar. I like Skratch Labs  which, like Gatorade, is perfectly balanced. Skratch Labs has a regular hydration drink but also a Rescue Hydration mix for those who know they are very depleted, expect heavy sweating, are salty sweaters, or expect heavy play like tournaments. For instance, if I have two matches in a day, I will typically drink the hydration mix during play but then use the hyper-hydration mix after the first match to quickly rehydrate – along with water.

Drink Myths

  • Coconut water is a better “sports drink”. Actually, it does not have enough sodium and has excessive potassium.
  • Pickle juice is a good replacement. Based on evidence, Pickle juice can help with cramping because of the acidity from acetic acid rather than replacing the needed electrolytes. People suffering from heartburn or hypertension may find this can do more harm than good.
  • All sports drinks are the same. Some contain 8% CHO (carbohydrate) which can cause stomach upset. Gatorade and Skratch Labs are 6% CHO which is ideal.


Good nutrition is key. Athletes may need to increase their intake of saltier foods during training in hot/humid environments. If you eat a lot of processed foods, you likely get way more sodium than you need. Everyone is not the same. Some people are very heavy sweaters and some are salty sweaters. If you are getting headaches or feeling excessively fatigued after playing, you may not have your rehydration under control. Watch the color of your urine – it should be sunrise yellow. If it is a heavier yellow or has a heavier smell, you are likely dehydrated.

Hydration Guidelines

  1. DAY BEFORE: Hydration starts the day before the event. Start each day well hydrated. Avoid consuming things like soda and coffee that deplete hydration levels and eat well.
  2. PRE-EVENT: To ensure proper pre-exercise hydration, you should drink 2 cups of water or sports drink 2-3 hours before exercise AND another cup 10 – 20 mins before exercise.
  3. DURING EVENT: 8-10 oz every 20 mins of play at regular intervals of combination of water and Gatorade/Skratch. If you are a heavy sweater, you may require more sports drink.
  4. RECOVERY: This is CRITICAL and also where people drop the ball! Rehydration requires water, electrolyte replacement like Gatorade/Skratch Labs (6% CHO), and food. Ideally the athlete weighs themselves and the weight lost is restored within six hours. This requires about 3 cups of fluid/pound lost. This is highly individual and makes recommendations very difficult. Eat within an hour, including protein and carbs.

If you suspect you are dehydrated, get to a cooler/shady place, remove excess clothing/equipment, put cold packs under arms and groin area, and rehydrate with a sports drink. If symptoms are not rapidly improving, assume it has progressed to a dangerous level and immerse in a cold bath to cool body and call 911.

Muscle Cramps

There is a new product called Cramps Away that is becoming more widely used in professional sports including tennis (James Blake and The Stanimal). It is NSF Certified for sports because it is all natural. It is reported to provide complete resolution of cramping after swishing mouth with the substance for 30 seconds, swallow and cramps disappear in one minute. In fact you can continue playing and it will protect you from cramps for 2 more hours. The theory is that muscle cramping is coming from a neurological overload that occurs during intense play. It works during play or if you get cramps after play or during sleep. The implications of this product while amazing and helpful should not negate any advice for hydration and heat illness. Likely, when you are dehydrated, the muscle may be more at risk to cramp even if it is caused by neurological overload. The best discovery in my opinion is muscle cramps may not always be caused by electrolyte imbalance or dehydration as once thought. Because this product is natural it is certainly worth a try if you suffer from muscle cramping.


When an athlete consumes more water than necessary and/or sodium becomes diluted in blood stream it can cause cerebral and/or pulmonary edema. This is called hyponatremia (low blood-sodium levels). It can cause confusion, coma, convulsions. Symptoms include headache, nausea/vomiting, swelling of hands/feet, lethargy/apathy, agitation. This may require transport to ER because it is difficult to increase electrolytes without fluids. You can’t just replace water without electrolytes! This is not nearly as common as dehydration but it does happen and is very dangerous.


Let’s wrap it up. As usual…


Acclimitization and Hydration are key to avoiding heat illness. Follow these guidelines, stay healthy, and play your best. Good luck out there!


Use the information on this site at your own risk. It is meant as a public service and represents the author’s personal knowledge and beliefs, not to replace your own additional research, common sense or instinct. Medical information changes rapidly, and the author cannot guarantee the accuracy or currency of the content.


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