If you experience weight loss during a single bout of exercise in the heat, dehydration is the likely culprit. While weight loss during one exercise session might sound like a good thing, the cause of the weight loss can actually impair your performance and put your health at risk. Weight loss from a reduction in your body's fat mass takes longer than one workout session.
Defining Dehydration
Your body relies on a certain level of water in your system for a variety of physiological processes, one of which is maintaining your normal body temperature. You bring fluids into your body through ingested water, other drinks and some foods. An hour of exercise can use up about a quart of your body's water. If you don't replenish this water loss, your body can become dehydrated. Exercising in the heat utilizes even more water than normal, partly due to the increased sweat rate you will experience in a hot environment. Dehydration during long-duration workouts also often results in sodium and electrolyte losses.
Impaired Performance
Dehydration due to heat and lack of sufficient fluid intake can lead to poor performance with endurance and high-intensity exercise. Poor coordination and muscle fatigue are often associated with dehydration. The time before you reach exhaustion can also be reduced in the heat. You might feel energy draining faster or experience muscle cramps.
Additional Risks
If your body is unable to cool itself efficiently, you are at risk for heat exhaustion and heatstroke. These heat-related illnesses are quite serious and could result in death if untreated. The goods news is that they can be easily prevented if certain precautions are taken in advance. You should also pay careful attention to the signals your body sends you while exercising in the heat. Weight loss should be treated as a dehydration alarm.
Recommendations
Plan in advance for exercising in the heat. Allow yourself some time to acclimate by decreasing the intensity or duration of your first few workout sessions in a hot environment. It might take your body one to two weeks to adjust to higher temperatures. Keep an eye on your hydration. One way is to inspect the color of your urine. Typically, your urine should be a pale yellow color. Dark urine might indicate that you are not drinking enough. Another way to monitor your hydration is to weigh yourself before and after your workout. If you lost any weight during that one session, you need fluid replacement.
The general recommendations for exercise hydration include drinking 14 to 20 oz. of fluid two hours before you start exercising. During exercise, drink 7 to 10 oz. every 10 to 20 minutes. After your workout, drink 16 to 24 oz. for every pound of body weight lost. You might need to increase these amounts when exercising in the heat. For endurance or high-intensity activities, a drink that includes sodium and other electrolytes, such as a sports drink, might be advised.
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