Staying well hydrated: before, during and after exercise
The amount of sweat produced increases with the intensity of the exercise, but also with the temperature and humidity of the ambient environment.
Physical activity therefore results in increased water requirements that parallel sweat losses. If these hydration needs for exercise are not met, the body can enter a state of dehydration.
Dehydration during exercise is recognized as having a detrimental effect. Indeed, dehydration has been shown to increase both heart rate and body temperature3. For example, when plasma volume is reduced, the heart has to work faster to maintain delivery of oxygen and nutrients to the muscles.
Numerous studies, reviewed in the American College of Sports Medicine (ACSM),2 show that dehydration increases physiologic strain and perceived effort to perform the same exercise task, and that warm-hot weather increases this phenomenon. The ACSM also considers that dehydration above 2% of the body mass can degrade aerobic exercise performance, and therefore endurance performance.
This is why people are advised not only to ensure proper hydration during exercise, but also before and after, in order to match the water losses, without waiting for thirst to appear.2 For exercise lasting less than one hour, water is sufficient to cover the body’s needs.1
The American Academy of Pediatrics reminds parents and caregivers that “Water is generally the appropriate first choice for hydration before, during, and after most exercise regimens”.5