Adequate hydration is vital for optimal health and proper function of the human body. It is even more important during exercise since more energy is being expended, which causes a spike in body temperature, and therefore an increase in sweat resulting in fluid loss.
Why Is Water Important?
Water makes up approximately 60-70% of body weight. Water has many biological functions that we cannot live without. It breaks apart other molecules by interacting with the positive and negative charges of particles, which makes it a universal solvent (1). This allows water to help cells transport and use nutrients and oxygen all throughout the body, it supports cellular structure, takes part in cellular reactions, and helps maintain acid balance.
It is recommended to be hydrated before exercise. Euhydration is the state of being in water balance. Fluid loss of greater than 2% body weight is considered dehydration, which negatively affects cognition and exercise performance (2). Severe dehydration, which leads to hypohydration of 6-10% of body weight can result in a decrease in cardiac output, blood flow to skin and muscles, and sweat production. To achieve optimal water status prior to exercise it is recommended by the American College of Sports Medicine to consume a fluid volume of 5-10 ml/kg of body weight 2-4 hours before exercise that results in pale urine color (2). For loss of >1.2 L/hour or workouts that last for more than 2 hours, it may be beneficial to also ingest sodium, which helps retain fluid (2). Sports drinks can be a good way to take in water and electrolytes for longer workouts.
The amount and rate that a person sweats is variable on the type and intensity of workouts and is different for everyone. Ideally, a fluid loss should be kept to less than 2% to prevent dehydration. It is just as important not to over hydrate with water or other low-sodium drinks, which may cause low sodium levels in your blood. Over the past few years, there has been an increase in overhydration among recreational athletes. If you drink at a rate that exceeds fluid loss through sweat, it may cause water intoxication and low sodium levels (2). If not treated immediately severe cases of under and over-hydration can be life-threatening. For most athlete’s an intake of 0.4 to 0.8 L/h is sufficient, however, this is dependent on the athlete and should be individualized to suit their needs (2). If you have a high sweat rate greater than 2 L/hr, your sweat is salty, or you will be exercising for 2 hours or longer you should be ingesting sodium (2).
Depending on how long and how intense your workout is the goal is to improve fluid balance and restore sodium levels. After exercising it is common to be in a fluid deficit and even after you finish your workout you may keep sweating and losing fluid through urine loss (2). The National Athletic Trainers’ Association recommends rehydrating and refueling within two hours after exercise (3).
To help maintain adequate fluid have water and other sports drinks easily accessible before, during, and after exercise to hydrate appropriately. For most workouts less than one hour, hypohydration is not as likely, however, each individual is different, and nutrition and fluid needs should always be customized. Make sure you reach out to a trained professional or registered dietitian to help you address your fluid needs so you can optimize hydration for better workouts.
- Sargen, M., 2021. Biological Roles of Water: Why is water necessary for life? – Science in the News. [online] Science in the News. Available at: <https://sitn.hms.harvard.edu/uncategorized/2019/biological-roles-of-water-why-is-water-necessary-for-life/> [Accessed 15 April 2021].
- Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance [published correction appears in Med Sci Sports Exerc. 2017 Jan;49(1):222]. Med Sci Sports Exerc. 2016;48(3):543-568. doi:10.1249/MSS.0000000000000852
- McDermott BP, Anderson SA, Armstrong LE, et al. National Athletic Trainers’ Association Position Statement: Fluid Replacement for the Physically Active. J Athl Train. 2017;52(9):877-895. doi:10.4085/1062-6050-52.9.02