Temperatures are on the rise across the country this summer! Here in Phoenix, I look like the red angry face emoji about 30 seconds into every one of my runs. Even at 5 am. It’s brutal.
That said, you’re probably already sick of hearing people tell you to hydrate when exercising outdoors. You know you need to hydrate, but how much fluid do you really need? And do you need the electrolyte drinks that are advertised relentlessly?
The truth is your water and electrolyte needs are highly individual. Your sweat rate, how salty your sweat is, and the climate you’re exercising in all play a role in how you should hydrate.
While there are no hard and fast rules for hydrating in the heat, keep reading to find out how you can determine what your body needs.
Why Do We Need Water?
For the average person, roughly 55-60% of your body is water. Water is used for everything from transporting oxygen and nutrients throughout the body to flushing waste and toxins to helping with absorption of certain vitamins and minerals.
Water is the single most important nutrient you consume. Think about it: you can live roughly 1 to 3 weeks without food, but you can only last a few days without water.
That said, it doesn’t take a complete lack of water for days on end for you to start to feel the effects of not hydrating sufficiently.
The dangers of dehydration range from mild to severe, but all are unwelcome. The most common consequences of dehydration include decline in performance, fatigue, confusion, fast heart rate, and low blood pressure. In severe cases, organ failure and death can occur.
What is Dehydration?
When you exercise, you lose fluid through sweat. Since sweat is our body’s built-in cooling system, higher temperatures mean more sweat and, therefore, more fluid lost.
When you don’t drink enough fluid to keep up with sweat losses and you lose enough fluid to cause weight loss, you are dehydrated. (1) Dehydration causes strain on the cardiovascular system, leading to impairments in exercise performance, cognitive function, body heat regulation, and even immune function. (1,2,3)
Dehydration can sneak up on you if you’re not careful, and the signs aren’t always obvious. So how do you know if you’re dehydrated? Studies have shown that urine color is a good indicator of hydration status. (1) Pale yellow is the ideal color, with progressively darker shades of urine indicating declining hydration status. Check your urine color against the chart below to find out if you need to drink more.
General Daily Fluid Needs
As noted, fluid needs are highly individual and, for this reason, there really are no standard guidelines for fluid intake. That said, The U.S. National Academies of Sciences, Engineering, and Medicine suggest that 2.7 liters per day for women and 3.7 liters per day for men is adequate to avoid negative effects from dehydration in the average adult.
It is estimated that water losses from sweat can range anywhere from 0.3 liters per hour during inactivity all the way to 2.4 liters per hour while exercising in heat. (3,4) To avoid dehydration, it’s important that you not only start any exercise sufficiently hydrated, but also that you maintain hydration during longer bouts of exercise and replace what is lost afterward.
How Much Water Should You Drink Before a Workout?
Rather than continuing to say “it depends”, let’s discuss some good rules of thumb, shall we?
Generally, you should start by drinking 5-10 milliliters per kilogram of body weight (2.3-4.5 mL/lb) within a few of hours of beginning exercise. For a 130-pound person, this equates to 10-20 ounces of fluid. (3)
Be sure to get those fluids in with plenty of time to use the restroom before starting exercise. You should then assess your urine color and continue drinking until it comes out pale yellow. If you’re a heavy sweater or you’re doing your workout in heat or humidity, including sodium in your pre-workout snack or fluids can help you retain some of that water. (3)
Try starting with 16 ounces of fluid 1-2 hours before your workout, then if you still need a bit more and can tolerate it, drink another 8-10 ounces 20-30 minutes before you start your sweat session.
Drinking Water During a Workout
As previously mentioned, fluid losses during exercise can be as much as 2.4 liters per hour. Factors that affect how much fluid is lost include duration and intensity of exercise, heat and humidity, altitude, your individual sweat rate, and fitness and acclimatization level. (3)
The goal of fluid intake during exercise is to limit overall fluid losses to less than 2% of your body weight. Every kilogram (2.2 pounds) of weight lost equates to about 1 liter of fluid. The average intake for most athletes while exercising is about 0.4-0.8 liters (14-28 ounces) per hour. (3) Sipping on fluids every 15 minutes or so helps you get the hydration you need without sloshy stomach from gulping it all at once.
In the absence of a better method, the best way to nail down your individual fluid needs is to regularly weigh yourself before and after workouts of varying intensities and in different environmental conditions. Using 1 liter of fluid for every 2.2 pounds of weight lost, you can come up with a pretty close estimate of how much fluid you lost during your workout and increase your intake by that amount. (3)
In addition to water, sweat also contains sodium and small amounts of other electrolytes. When exercising for longer than 2 hours, at high intensity, and/or in heat or humidity, OR if you sweat a lot or have salty sweat, you may need sodium during your workout as well. (3)
Aaaannd…let’s not forget that increased body temperature and sweat production also increases how much glucose is used to fuel your body. Having a sport drink with some carbs or carb-based nutrition during long workouts (>90 minutes) is always a good idea.
On the flip side, it’s important to note that overhydration can lead to low blood sodium levels, which can cause nausea, vomiting, cramps, fatigue, confusion, or worse. (3) Until you nail down your hydration needs, you should include sodium in your fueling and hydration plan for workouts longer than an hour in heat and humidity. Good options include salt tabs, salty snacks, or electrolyte drinks.
What to Drink After a Workout
I probably don’t have to tell you that you continue to sweat after you finish a workout. As such, the amount of fluid needed to rehydrate after exercise is greater than fluids lost during the workout. Roughly 125-150% greater, in fact. (3)
As the primary electrolyte lost through sweat, sodium should be part of your rehydration plan after a sweaty workout as well. But unless you have incredibly salty sweat, you don’t need to drink from the salt shaker. A post-workout snack with salt or an electrolyte drink should suffice for most athletes. (Note, if you think you do have unusually salty sweat, consider getting tested to determine your needs).
Hydration is incredibly important for all humans, and athletes have special considerations for maintaining adequate fluid levels.
Each athlete has unique fluid needs that are impacted by several factors. Such factors include fitness level, duration and intensity of exercise, sweat rate, sodium content of sweat, acclimatization to the environment, and environmental conditions (i.e. altitude, heat, humidity).
It’s always important to hydrate before and after workouts. And if you’re going for a particularly sweaty workout – whether due to duration, intensity, or environmental conditions for the workout – it’s also important to have a hydration plan during exercise.
If you need help nailing down your fuel and hydration needs and want to learn more about working with me, send me a message!