When I work with any athlete, one of the first questions I ask is, “what is your sweat rate?” Ninety-five percent of the time, I get a blank stare. When creating a performance nutrition plan, knowing your sweat rate is critical to make sure fluid replacement during exercise is adequate (but not too high). Here is why.
The Importance of Water
Water plays major roles in the body at any given time, but especially during exercise. During exercise, water inside your body cools your core and muscles, keeping you from overheating too quickly. This helps you perform stronger and longer. In addition, water transports nutrients to your muscle for use in exercise metabolism and then cleans up by transporting metabolites away from your muscle to be filtered and excreted. Water plays a key role in preventing dehydration, which also keeps the athlete mentally “on” throughout the workout. Finally, water acts as a cushion to your organs to protect them in case of impact during sports.
Why You Should Know Your Sweat Rate
What I refer to as a sweat rate is defined as exactly how much water an athlete loses per hour of exercise. It is important to know your number because sweat rates vary widely from athlete to athlete. Females generally range from 2-5 cups per hour and males range from 4-7 cups per hour. However, variables such as air temperature, humidity and amount/type of clothing can change sweat rate day to day. Once I know an athlete’s sweat rate that tells me how much fluid per hour we need to replace during exercise.
How to Calculate Sweat Rate
To figure out your sweat rate, pick a workout that is at least one hour long. Weigh yourself before and after that workout. Do not pee during the workout (unless you want to measure it), and keep track of how much fluid you take in during that workout. After the workout ends, take a look at how much weight you lost compared to how much fluid you drank. If your weights are about the same before and after, the amount of fluid you drank matched how much fluid you lost in sweat. If, however, your weight dropped during the workout, you did not drink enough fluid and need to increase your intake next time. By using this simple method, you can easily estimate your sweat rate. When doing this test, it is a good idea to note temperature and humidity during the test for future reference. Be sure to do separate biking and running tests, as most athletes have a different rate for each.
Hydration
Hydration is crucial during exercise, especially exercise lasting more than 1 hour. When we are not working out, fluid is primarily excreted from the body through urine. When we are exercising, fluid excretion shifts largely from urine to sweat (note to athletes who do not consume adequate fluid before and during exercise in fear they will have to frequently stop for bathroom breaks). Because there are many factors affecting sweat volume, weigh yourself before and after exercise throughout the year as your climate changes. Journal your findings to pinpoint differences based on environmental factors and note trends in fluid loss. To replace fluid, replace 1 pint (16 ounces) of fluid for every pound lost. If you are losing 2 percent body weight or less you are replacing correctly. If you are losing more than 6 percent body weight you are at a greater risk for heat exhaustion, heat stroke, severe heat cramps and even coma or death.
To start determining your needs, start with a goal of 24-32 ounces an hour. Calculate the weight change and start your workout already hydrated. How do you know you are hydrated? Your urine is a pale yellow. Do not rely on thirst to determine when to consume fluids, but determine your specific needs and drink at regular intervals throughout exercise. I recommend every 15-20 minutes.
Electrolytes
The following ions are electrolytes: sodium, chloride, potassium, magnesium, calcium, phosphate and bicarbonate. Electrolytes and water go hand in hand: where there is a high concentration of electrolytes, water follows, so both need to be replaced during exercise. This is because electrolytes need water to conduct electricity regulating hydration, muscle and nerve function and acid-base balance. Pertaining to athletics they also improve cognitive function, performance, reaction time, muscle cramp frequency and recovery. Through my research I noted that consuming branch chain amino acids (BCAAs) and arginine/glutamine supplemented the effectiveness of these results. The primary electrolytes lost in sweat are sodium and chloride compared to potassium, magnesium and calcium.
Knowing the concentration of electrolytes each athlete needs to replace during exercise is not as easy to determine as fluid needs. Just as you should start exercise hydrated, you need to start exercise with electrolytes in your system. This can be consumed through a salty snack or a beverage containing electrolytes, like Gatorade. What to consume during exercise depends on the intensity and duration. Typically you do not need to start replacing electrolytes until about 1 hour after starting. After 1 hour, add electrolytes to your water or consume in the form of food. Companies have come up with some great products that contain electrolytes and others that contain a combination of electrolytes and carbohydrates, either in the form of fluid or food. Experiment what works best for you by consuming different forms of the three elements you need when exercising: water, electrolytes and carbohydrates.
