Physical exercise can elicit high sweat rates and substantial water and electrolyte losses that compromise exercise performance. In general, we consume food and fluid during exercise to provide energy, delay fatigue, prevent or delay dehydration, replace electrolytes and minimize gastrointestinal distress. But how much fluid to rehydrate with during exercise?
Significant differences in sweat rates between sports, individuals themselves (affected by genetic predisposition, heat acclimatization and training status, at a minimum), exercise duration, climates, and other factors, affect this determination. Individualized rehydration plans need to take account of all of this. Athlete tables can be used to help approximate weight loss depending on your size and activity (and I work with clients to make those estimations). You can also just weigh yourself immediately before and after your workout to determine how much weight you are losing during a typical workout at the gym (you will always need to do this more than once but that is particularly true if working out outdoors as climate, including humidity and wind, terrain and precise metabolic requirements for your particular exercise will all affect your fluid loss workout to workout). The goal is to avoidexcessive weight loss, which refers to a loss of > 2% of body weight. For each pound of water weight lost, you’ll want to drink about 20 ounces of fluid. You won’t necessarily be able to drink that much during your activity, but drinking at least some of that will help minimize that excessive weight loss.