Stay Hydrated During Physical Activity!

Kimberly McGrath, Ph.D., CISSN

Regardless of your fitness routine (perhaps enjoying Poway’s beautiful trails or in one of our amazing local fitness or martial arts studios) staying adequately hydrated is critical to be at your best.

Water is required for regulation body temperature and transportation of nutrients to into our cells and transport of waste out of our cells, not to mention cognition and brain function and joint flexibility, and muscle contraction.

Our muscles are approximately 75% water. Related to exercise, blood flow to exercising muscles is reduced with dehydration, leading to impaired performance. Appropriate water intake to limit dehydration is the single most effective way to maintain exercise capacity during your training. Typical rates of sweating during exercise are between 1.0-4.4 lb./hour[i] and performance can be impaired when as little as 2% of your body weight is lost through sweat. It’s possible to feel performance impairment even during <1h of exercise – especially at elevated temperature. When dehydration levels get closer to 4%, we are at risk heat exhaustion and heat stroke.[ii]

People do not typically get thirsty until they have already lost a meaningful amount of fluid through sweat. Thirst is a LAGGING indicator of hydration status, meaning that if we become very thirsty, we’re already at least slightly dehydrated.

• A practical rule of thumb for recommended daily water intake is 0.5 to 1 oz. per lb. of body weight – on the lower end if you are sedentary, on the higher end if you regularly go to the gym. (e.g. if you weight 150 lbs and are highly active, target about 150 oz. per day).

• It’s a great idea to establish habits that generally improve water intake and hydration around your exercise. A starting point is 16 oz. upon waking, and another 16 oz. about 30 minutes before exercise.

• During exercise, consume in the range 16 - 70 oz./hour of fluid to offset water loss. This range is wide and will depend on your size, climate, and exercise intensity. If you are able, sip every 5-15 minutes versus larger quantities and longer time intervals between drinking.

• For high intensity exercise extending 90 minutes or more, it becomes increasingly important to ensure fluid regulation and fuel supply. In this case, sipping a drink containing electrolyte and carbohydrates (for example, Pedialyte) every 10–15 min throughout exercise is advisable.

• After exercise, seek to completely replace all the fluid and electrolytes you lost during your training session. Consider an electrolyte and carbohydrate drink instead of simply water. Addition of some salt to your after-work out snack can support rehydration.

How do you know if you are hydrated? A peek at your urine is the easiest way to know. Ideally the color should be faint/pale yellow. Here’s an easy chart to identify the right color for hydration.

Kim McGrath, Ph.D., CISSN is a local Personal Nutrition Coach and Sport Nutritionist. Email: kim@modus-energy.com Instagram: @kmcgrath.phd

[i] Maughan RJ, Noakes TD. Fluid replacement and exercise stress. A brief review of studies on fluid replacement and some guidelines for the athlete. Sports Med. 1991;12(1):16–31.

[ii] Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American college of sports medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377–90.