Your body is so efficient at many processes, but needs water (hydration) to do most of them. One of the greatest ways we lose fluid from our bodies is through sweating. Our bodies try to cool down by dissipating heat during exercise in the form of sweat. This causes changes in the amount of hydration and electrolytes a person has, and can affect athletic performance and health.
To maintain optimal fluid balance, you need to replenish the fluid lost. The rate of fluid loss during exercise is affected by the type of sport, duration, intensity, temperature, wind, humidity and types of clothing you are wearing. All of these factors, as well as the differences between peoples’ fitness levels, makes it harder to provide specific guidelines for fluid replacement.
If you are an athlete training or heavily exercising, you may want to monitor your body’s weight changes during exercise to calculate how much fluid you are losing. From there, you can determine how much fluid you need to replenish your body. Weigh yourself early in the morning before getting dressed to determine your baseline, and then after a specific time of exercise. Subtract your body weight after your workout from your pre-workout weight. If you drank beverages during your workout, this also needs to be added in.
Physiologic stress increases when you are dehydrated. You measure physiologic stress by core temperature, heart rate, and perceived exertion. The more water you lose, the more physiologic strain is experienced by your body. This impairs both mental and aerobic performance. Your aerobic performance decreases when you’re dehydrated because of the increase in your cardiovascular strain, core temperature, need for glycogen, and changes in your metabolic functions. This affects your ability to concentrate, do skilled tasks or strategically plan. You become at risk of heat exhaustion and/or heat stroke, skeletal muscle cramps, or in some long endurance events, hyponatremia (low sodium level in the blood).
Prior to exercise, hydrate so that you start physical activities with normal hydration and electrolyte levels. Consuming liquids hours before you start exercising ensures that your bodily functions will not be compromised.
During exercise, monitor how you feel. If you are exercising at a high intensity for long periods of time, check for weight changes. Make sure to replace fluid and electrolyte losses during and after exercise over the next 24 hours. Drink 1.5 liters of fluid for every kilogram lost or 24 ounces for each pound. This rate of 150% of sweat losses is required because of the additional urine output that will occur from increased intake.
Some people find it hard to drink enough water to meet their needs. Beverages that are flavored with natural lemon, cooled and containing sodium may enhance the voluntary intake. Another trick is to fill up liter bottles (like blender bottles) with your daily fluid needs every morning and put them in your refrigerator, so you can visually see how much you need to consume and easily track.
Dehydration can have serious side effects, so always work hard to make sure you are consuming enough fluids throughout the day and electrolytes during high-intensity exercise.