Most athletes have a sense – or at least they have figured out through trial and error – which foods and mealtimes work best for them. But paying attention to fluid intake is sometimes overlooked, and athletes rely on their thirst mechanism to ‘drive them to drink’.
But that may not be enough. By the time we get thirsty, we may have already lost up to four cups of fluid – enough to impair not only performance, but our ability to keep ourselves cool.
Along with heavy exercise comes heavy sweating – it’s the body’s way of dissipating the heat that is produced through activity. Environmental conditions affect how much we sweat - as temperatures and humidity go up, so does the amount of sweat that is produced. Athletes can lose anywhere from four to 10 cups of fluid after an hour of intense activity when it’s hot and humid. When the air is dry we still sweat, but it evaporates so quickly we are less aware of it.
Those who exercise at high intensity or under hot or humid conditions often teach themselves to drink on a schedule, because the thirst mechanism might not kick in until they’ve lost close to four cups of fluid. Many athletes keep track of their weight before and after exercise so they can figure out how much to drink. Every pound of weight lost through sweating is the equivalent of about two cups of fluid that needs to be replaced.
Without adequate fluid replacement, fatigue sets in– and there’s also the risk of dehydration and heat exhaustion. Exercise performance is impaired once fluid losses reach about two percent of body weight – that would be the loss of about three pounds of fluid during a bout of exercise for a 150-pound athlete.
But sweat is more than just water. Sweat contains sodium and chloride – the same compounds that make up table salt. These salts – often called electrolytes – also need to be replaced to reduce the risk of heat-related muscle cramps and heat exhaustion. Potassium and magnesium are other electrolytes that are lost through sweating, although we don’t lose nearly as much of these as we do sodium and chloride.
Sports drinks are great any time, but are particularly important if exercise is going to last longer than an hour. They are specially formulated to provide small amounts of carbohydrate to keep muscles fueled, and they contain all-important electrolytes to replace those lost through sweating. They also taste great – which means you’re more likely to drink them.
Here are some general guidelines for fluid intake for athletes:
- Drink about two cups of water or a sports drink two to three hours prior to exercise
- Have another two cups or so of water or sports drink 10 to 20 minutes before starting exercise
- Drink six to 12 ounces every twenty minutes during activity
- Water is fine for short periods of activity, but sports drinks are recommended – especially if you are going to work out for an hour or more.
- For every pound of weight loss during activity, drink two cups of water or a sports drink.
Susan Bowerman is a consultant to Herbalife.