by Jennifer Novakovich
Exercising in the heat is a major challenge for the human body and its ability to regulate its internal environment. In an effort to restrict a rising core temperature, sweat production increases at the cost of water and electrolyte losses. While these losses are offset to a small extent by internal adaptations (e.g. increased heart rate), once dehydration sets in, body function, and therefore performance, will be reduced. With the summer heat in full swing, what steps can you take to maintain performance and continue to effectively train?
Before we get into how you can maintain performance, here are some basics about the physiology of exercising in the heat. During exercise, only about 25% of the energy released by the muscle is actually used to do work (e.g. pull, push, jump, etc.). The remaining 75% is simply heat lost from the body. When outside temperatures increase, on top of the above heat produced, heat will be gained. Again, this is a major challenge for the human body and sweating is a tactic to dissipate heat and limit the rise of core temperature. Sweating leads to the loss of both body water and electrolytes (especially sodium). While small loses are well tolerated, dehydration and electrolyte depletion will eventually lead to reduced performance and an increased risk for heat illness and the incidence of muscle cramps. Furthermore, there is evidence that exercising in the heat also leads to a faster depletion of glycogen stores and ultimately reduced cognitive performance and endurance. During exercise, mid-, pre-, and post- workout beverages or snacks should contain carbohydrates in order to maintain and replenish glycogen stores.
Clearly dehydration is a major consideration when trying to maintain performance; how much do you really need? Daily water turnover for sedentary individuals in temperate conditions is typically 2–3 liters; these losses are increased in the heat. Sweat losses during exercise can add 0.5–3 liters per hour depending on the intensity of the exercise, clothing worn, conditions, and the individual. As a result, fluid requirements will increase to match the demands of the exercise. Fluid intakes should be enough to restrict body mass losses to 2% of an athlete’s pre-exercise mass. Athletes should also avoid drinking so much that they gain mass during exercise. The best thing to do would be to listen to your body and drink as thirst indicates. If that’s not a reliable method for you, checking the color of your urine may be a good idea (aim for light to clear colored urine). On a final note, adaptations to hot conditions will occur, even within a few sessions, and as a result, athletes may be tempted to reduce fluid intake. In reality, heat acclimatization actually increases fluid requirements by increasing the sweating response.
Aside from dehydration, electrolytes are also a major consideration while exercising in the heat. Despite this fact, many people are confused by why electrolytes are important. What are they and how do the affect your performance? Electrolytes are essentially salts that are electrically charged. They can either be positively charged (+, cations) or negatively charged (-,anions) which ultimately affects how they interact with each other in your body. The major electrolytes in the human body are sodium (+), potassium (+), Chloride (-), calcium (+), magnesium (+), bicarbonate (-), phosphate (-), and sulfate (-). Sodium is the major cation outside of cells while potassium is the major cation inside of the cell. These two electrolytes in particular are vital for maintaining voltage gradients across cell membranes and the generation of electric impulses, making them essential for nerve function and muscle contraction. Mild electrolyte deficiencies will lead to fatigue, muscle spasms, cramping, etc. Electrolytes are therefore critical when trying to maintain performance.
When you exercise, especially in the heat, electrolytes are lost through your sweat (particularly sodium and potassium) and must be replaced. If that’s the case, should you consider taking an electrolyte replacement like Gatorade (also high in carbohydrates)? The answer really depends on a number of factors including your diet, the intensity of your workout, the time spent exercising, and the temperature.
Electrolytes shouldn’t be a huge concern for most athletes and can typically be maintained through a well-balanced diet with adequate servings of fruits and vegetables. Salt is generally not a huge concern either since the typically westernized diet contains about 3.4g of sodium daily (an amount demonstrated to increase risks for heart disease). The minimum amount to maintain proper function is about 500 mg and the recommended intakes are no more than 2.3g. As a result, electrolyte replacement drinks would be best limited to only exercise exceeding an hour or for athletes on a salt-restricted diet.
Instead of taking an electrolyte replacing drink during exercise, a better option would be to simply increase the electrolyte rich foods and drinks in your diet. Coconut water and bananas make for an excellent, all-natural, electrolyte replacement. Increasing your consumption of leafy greens, nuts, seeds, fruits, and vegetables is also a good idea when trying to maintain electrolyte balance. Sunwarrior Liquid Light is a great electrolyte replacer that can be added to water, juice, or smoothies. My go-to electrolyte replacing drink is a mixture of Sunwarrior’s Supergreens and coconut water—a tasty way to stay on top of my game in the heat.
My final consideration is keeping cool (as cool as you can anyway). Choosing the right clothing can go a long way in terms of heat dissipation. For example, choosing lighter colored clothing, modern synthetics, or less clothing in general would be good ideas when deciding what to wear. Warming up (slowly!) in the shade and staying in the shade as long as you can would be another consideration. If possible, avoid working out at the hottest time of the day and aim for either early morning or evening. Pre-, mid-, and post-workout cooling also go a long way in terms of performance and fatigue. Cool, wet towels, spray bottles, and cold beverages are effective ways to cool off while exercising.
With summer in full swing, measures to keep cool, healthy, and hydrated are essential when trying to stick to a workout regime. With the proper knowledge about exercising in the heat, there is really no reason to put a damper on your training programs. Furthermore, with proper preparation, you can continue to perform well during hot and sweaty conditions.
Grantham J, Cheung SS, Connes P, Febbraio MA, Gaoua N, González-Alonso J, Hue O, Johnson JM, Maughan RJ, Meeusen R, Nybo L, Racinais S, Shirreffs SM, Dvorak J. (2010) Current knowledge on playing football in hot environments. Scand J Med Sci Sports. 20 Suppl 3:161-7. Kenefick RW, Cheuvront SN. (2012) Hydration for recreational sport and physical activity. Nutr Rev. 70 Suppl 2:S137-42. Maughan RJ, Shirreffs SM, Ozgünen KT, Kurdak SS, Ersöz G, Binnet MS, Dvorak J. (2010) Living, training and playing in the heat: challenges to the football player and strategies for coping with environmental extremes. Scand J Med Sci Sports.20 Suppl 3:117-24. Mora-Rodriguez R, Hamouti N. (2012) Salt and fluid loading: effects on blood volume and exercise performance. Med Sport Sci. 59:113-9. See this and other articles on Jennifer Novakovich’s website JennovaFoodBlog.com
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