General Health & Wellness

Master Your Fluid Balance to Beat the Heat

For some, the feel of your own sweat rushing down your face from physical exertion can be uplifting and motivating. For others, the thought of clammy skin and sticky, sweaty clothes is enough to deter you from even stepping foot out of the comforts of your 70° ice house without having your car on auto start (twice) just to avoid the summer heat.  Here’s how you can safely workout outdoors and be [relatively] comfortable at the same time!

First off, don’t fear sweat! We can often reduce our anxiety and stress over a situation by changing our way of thought around a particular topic.  Sweat is the human body’s way of cooling off when exposed to hot environments or during periods of increased metabolic activity such as exercise or sports.  It helps us stay cool and performing our best.  Sweat is good!  We have a highly adaptive body that can learn to survive in some of the most intense and stressful environments.  While 90+° weather should not be taken lightly when planning outdoor exercise, with the right preparation and monitoring, you will survive and you will grow stronger for it. This year, you won’t use the heat as an excuse to stay indoors. It’s time to master your fluid balance.

Water bottlesFluid balance is the ratio of fluid entering your system (through food and drink) and fluid exiting your system. On average, we consume 1L (4.23 cups) of water daily, although it’s recommended we consume a minimum of 6-8 cups for every 100lbs of body weight1.  Another way of looking at would be to take half of your weight in pounds, and consume that many ounces of water daily.  On the flip side, fluid loss occurs primarily from evaporation, breathing, sweating and going to the bathroom.  In these cases, if fluid is not replaced, you will lose plasma volume in the blood forcing the heart to work harder to pump more blood throughout your system to maintain cardiac output. This will inevitably lead to premature fatigue, and if not cared for, even more dangerous situations such as heat stroke.  Symptoms to look for to prevent serious illness include vomiting, nausea, headaches, dizziness, fainting, rapid heart rate, and even constipation amongst others.

Your body loses the majority of its fluids through evaporation from the skin and respiration. In the presence of increased humidity, excessive or too tight clothing during exercise, your body’s ability to sweat and cool off will be greatly reduced, which could also increase your risk of heat related illness2.  In regards to respiration, to further cool your body your can expect to breathe heavier outdoors when performing the same relative work load as you did indoors.  More fit individuals will adapt quicker to this change in environment. However, an acclimation period of 10-14 days would be appropriate for less fit individuals2.  Over this time frame, gradually increase your exposure to the heat to allow your body to further adapt its evaporation and respiration rates, and therefore ability to cool off outdoors.  If possible, exercise during cooler parts of the day before gradually working towards warmer and longer periods of time outside in the heat.

If you’re using thirst as an indicator of fluid balance, then you’ve already lost 1-2% body weight and well on your way towards trouble if you don’t hit the brakes and change course by rehydrating before resuming. If you’re excessively dehydrated, you can safely consume 4-6 cups of water per hour until your body weight has returned to its previous healthy weight1.  Ideally, I would recommend you consciously increase your water intake 1-2 days prior to beginning your outdoor venture to match the ½ body weight goal mentioned above.  (Less time if you’re closer to the above mentioned daily goal, more if you’re sole source of water is whatever hits your mouth in the shower.)  From there, to maintain your hydration, consume roughly 1 cup of water during every 15 minutes of exercise and activity.

Preparing your body by increasing water intake days before heading outdoors will prevent another source of fluid imbalance caused by relatively low electrolyte levels in the blood. We lose electrolytes along with our sweat at a much slower rate as compared with body water. If you consume enough pure water in a short enough period of time due to intense thirst from rapid water loss, your level of electrolyte concentration would be relatively low compared with your body water level.

Sodium and potassium are the two more commonly known electrolytes, however equally important are magnesium, chloride, calcium and chromium. These minerals all carry an electrical charge when dissolved in water to help fluid pass through the body to where it needs to go, and are essential for proper muscle contraction, nerve impulse transmission, and fluid balance.  Not only would it be wise to supplement your water with a concentrated electrolyte mix that contains all of these minerals (sorry, not talking about Gatorade or PowerAde), I would also recommend searching for food sources to include in your normal diet that would bump these levels up.  Examples include various nuts and seeds, dark leafy greens, broccoli and even meat or dairy.

Normal plasma sodium concentrations fall between 136-145mEq/L1.  While you can’t necessarily take a blood sample on the go to test your levels, assessing your urination frequency and urine color is a good “field test”.  When your urine color is colorless to a pale yellow, you are most likely in good fluid balance and would be safe to venture outdoors.  If you have not been urinating regularly (several times per day), or if your urine is a dark yellow, I would suggest hydrating in advance before going outdoors.  If your urine has a light or dark brown color to it, you are dehydrated and should definitely avoid the heat for now.

For those endurance athletes with events lasting longer than 90 minutes, consume an additional 20oz of water with 30g of carbs and electrolytes and 15g of protein mixed in roughly 30-60 minutes before heading outdoors. Maintain your hydration by consuming this ratio for every hour of sweating but sip gradually as to make it last. Higher concentrations of these nutrients and minerals could possibly lead to digestive distress, so more is not necessarily better in this case.  If you plan to return outdoors again soon and want to continue performing your best, it would also be wise to repeat your pre-workout supplement protocol after you’re done1.

In the end it is critical to maintain proper fluid balance to optimize performance, which may require increased water consumption, proper supplementation and clothing, as well as an acclimation period to transition outdoors. The heat should not be taken for granted, but it should also not be feared.  You can train year round and enjoy the seasons at the same time.  Now you know how to beat the heat, so cross that excuse off your list.


1. The Essentials of Sport and Exercise Nutrition, 2nd Edition; John Berardi, PhD; Ryan Andrews, MS, MA, RD


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