Hydration Update: Sports drinks, Sweat Rate & Caffeine
I always like to attend (and present at) sports medicine conferences. Before the Boston Marathon, I enjoyed the American Medical Athletic Association’s sports medicine meeting and particularly liked the hydration talk presented by Brendon McDermott PhD ATC, assistant professor at the University of Arkansas. Here are some key pointers:
• The main audience for sports drinks is not athletes but the average person, especially kids. The selling of sports drinks is a big business, targeted to a much larger audience than athletes to get many more sales. Yet, proper hydration is indeed an issue for athletes. McDermott, who is chair of the upcoming National Athletic Trainers’ Association’s Position Statement on Fluid Replacement for the Physically Active, reported that 65% to 85% of athletes come to a game or practice underhydrated.
• Athletes, particularly those who sweat heavily, learn their sweat rate by weighing themselves (nude) before and after a one-hour workout. Any weight loss reflects water (sweat) loss. Normal thirst prompts athletes to replace only 2/3 of what gets lost during exercise.
• If your weight drops two pounds during a workout, you have lost 32 ounces (one quart) of sweat. Some athletes may lose only half a quart (16 ounces) of sweat during an hour-long workout; others may lose four quarts. Your goal should be to lose less than 2% of your body weight during exercise (three pounds for a 150-pound athlete). Weighing IN and weighing OUT is a good way to learn how well you balance your fluid intake.
• The problem with inadequate fluid replacement is, as you get dehydrated, you feel worse, slow down, and perform worse. While many people think that dehydration causes internal body temperature to rise, McDermott said that is not always the case. The intensity of exercise is the main predictor of body temperature. You can be well-hydrated but still get over-heated.
• Caffeine is not dehydrating. Yes, caffeine increases short-term urine production, but it does not lead to dehydration. Here’s why: Caffeine stimulates the bladder to contract; this increases the urge to urinate. This water (urine) in your bladder has already been used by your body. Hence, coffee stimulates the bladder to empty sooner —but you do not need more fluid than if you had consumed a caffeine-free beverage.
For more information, read the chapter on Fluids in my Sports Nutrition Guidebook and my Food Guide for Marathoners; Tips for Everyday Champions