Hydration - New Fluid Replacement Recommendations from ACSM


The American College of Sports Medicine (ACSM) recently updated their position on how to best hydrate before, during and after exercise.1 Is your hydration strategy up to speed? Read on to find out what the experts are saying.

Is hydration important to performance?

Absolutely! Exercise generates internal heat. To function at your best athletically, that heat needs to be released. As your internal temperature rises, your body responds by increasing blood flow to your skin and initiating sweating. More blood flowing to your skin transfers heat away from your core and toward the exterior of your body where it can be released. The evaporation of sweat in warm or hot weather is the primary avenue for losing heat and so sweat losses can be substantial. Sweat is composed of water and electrolytes and if they aren’t appropriately replaced, dehydration can result. Conversely, if too much fluid is consumed, overhydration or hyponatremia can occur. Both dehydration and overhydration impair physical performance and can pose serious health risks. So, having a hydration plan is critical to athletic performance and important for your health.

Don’t zone out

On average, athletes typically lose anywhere from 500 to 2,000 ml (17 to 67 fl oz) of sweat per hour. That equates to roughly 1 to 4 pounds worth of sweat. You give yourself the chance to perform at your best if you don’t lose anymore than 2% of your body weight due to fluid loss during exercise.

So, if you weigh in at 150 pounds before exercise, you need to remain somewhere between 150 and 147 pounds during exercise to perform at your best. This 2% rule is called your hydration zone. Know it and stick to it. It’s a strategy that will pay dividends.

What happens when you exceed the 2% weight loss hydration zone is that the very same exercise you did yesterday with relative ease is going to feel more difficult to do. You’re going to have to strain to keep up the pace. Falling out of your hydration zone also affects your ability to think clearly and tactically, especially in hot-weather conditions. Give yourself every chance to be your best by hydrating sufficiently to stay in your hydration zone.

Know your sweat rate

A key message from the new recommendations is that sweat rates vary tremendously from one athlete to the next, and from one activity to the next. Athletes in the National Football League and cross-country runners can work in the same scorching heat and for the same length of time, yet football players typically lose over twice the amount of sweat as runners. Why the difference? Because fluid losses are determined by a variety of factors including body weight, type of clothing and equipment worn, and how acclimated athletes are to heat.

Sweat rates vary and you need to know your own because state-of-the-art hydration today means every athlete has an individualized hydration plan. In other words, the right hydration plan is based on your personal sweat rate, not the sweat rate of your training partner. One-size-fits-all fluid intake recommendations no longer fit; especially if top performance is your goal. To measure your sweat rate, use PowerBar’s online Hydration Calculator.You’ll be guided through a simple one- hour test workout that will calculate your sweat rate. Conduct the test workout at an exercise intensity and in climate conditions similar to the conditions you encounter during training and competition. Better yet, test yourself at different exercise intensities and in different climate conditions, and as your fitness level changes. By repeating sweat rate testing under varying conditions, you will better understand how your body responds to different conditions. This will help you fine- tune your hydration plans for whatever you encounter during training and competing.

Putting your sweat rate to good use

Knowing your sweat rate is half the battle. The other half is actually consuming the fluids you need and knowing what type of fluids to consume.

Lots of athletes find it difficult and uncomfortable to consume fluids at a volume that matches their sweat rate. If you are in that camp, don’t despair. Remember that your hydration zone is losing no more than 2% of your pre-exercise body weight due to fluid loss during exercise. So, you don’t need to exactly match your sweat rate. You just need to make sure that you don’t drop out of your zone while you are exercising.

Putting this into practice:

Let’s say you weigh 150 pounds, you lose about 2 pounds of fluid per hour during exercise according to your sweat rate test (~31 fl oz per hour), and you plan to compete in an event that will probably take you 3 hours to finish.

If you do the math, your hydration zone weight is between 150 and 147 pounds. Given your sweat rate, after the first 90 minutes of exercise you would be at the low end of your hydration zone, and you would drop out of your zone thereafter. However, by consuming fluid at just half your sweat rate (~16 fl oz per hour instead of 31 fl oz per hour) throughout the event, you could remain within your hydration zone for the full 3 hours of exercise.

The point is to know your sweat rate and hydrate strategically so that you remain comfortable and within your hydration zone. You may also be able to gradually train yourself to absorb more fluid during exercise. So, if you’re having trouble consuming enough fluids, start at a volume you are comfortable with, and gradually increase the volume consumed per hour during training until you reach a more acceptable level of intake.

Sport drink versus water and the lowdown on electrolytes

Water only contains fluid. A well-designed sport drink like POWERBAR® Endurance sport drink contains fluids, carbs, and electrolytes. Which drink is best for you depends on what you are doing and for how long.

For low-to-moderate intensity activities in mild conditions that are less than an hour in length, water is generally fine for rehydrating.

For endurance events of one hour length or longer, and for events in hot-weather, a sport drink is generally a better choice. The carbs in a sport drink can help sustain or extend your ability to perform athletically. The key electrolytes in a sport drink are sodium and chloride which together form salt. Of the electrolytes in sweat, these two are lost in the greatest amounts during sweating. Including these electrolytes in a sport drink helps you replace those lost from sweating, retain consumed fluid, and stimulate thirst. In addition, flavored sport drinks help increase the amount of fluid ingested compared to plain water.

Carbs and electrolytes can also be consumed in non-fluid sources like gels, energy bars, and other foods, just as long as they are paired with sufficient water to meet your fluid needs.

Finally, when it comes to caffeine, the ACSM recommendations indicate that the evidence available suggests caffeine consumption may help sustain exercise performance and it probably doesn’t alter hydration status during exercise.

How can you tell if you’re rehydrated?

Let’s say that yesterday’s workout was a long one, and in very hot conditions. You followed your usual rehydration and refueling strategy, but want to make sure that you’re fully rehydrated before engaging in another workout. What can you do?

According to the new guidelines, a practical method for assessing your hydration status or balance includes a combination of measuring body weight and evaluating urine color. The catch is that each method needs to be done properly.

Measure your body weight upon arising in the morning, after urinating, and compare this to your typical body weight. Your typical body weight should be the average of repeated body weight measurements taken in the morning. Changes in eating and bowel habits, and timing within the menstrual cycle can influence body weight, so multiple measurements are needed to establish a valid baseline value.

In addition to measuring body weight, urine color can be evaluated in the first morning urine sample or in a urine sample taken after several hours of stable hydration status. Downing large quantities of fluids after exercise can lead to the production of dilute urine long before you are actually fully rehydrated, so don’t be fooled by a urine sample taken soon after chugging a water bottle full of water or a sport drink. Testing your urine color several hours after actively rehydrating is advised. Urine that is dark in color (highly concentrated), is a sign that you’ve not yet fully rehydrated. The goal is a urine color that is light yellow in color, something close to the color of lemonade.

Hydrate before exercise

Before exercise, and when the timing is feasible, ACSM recommends that you consume fluids at least 4 hours before exercise. If you are well hydrated this should lead to urine production. If it doesn’t, or the urine that is produced is dark in color, you should drink more fluid about 2 hours before exercise. This will allow sufficient time for urine to be eliminated before starting exercise. According to ACSM, the amount of fluid to consume before exercise depends on your body weight:

Consuming a sport drink with sodium, small amounts of salted snacks, or sodium-containing foods at meals will help stimulate thirst and retain the consumed fluids. Also, fluids that are cold in temperature, contain some sodium and carbs, and are flavored can enhance the appeal of beverages and help promote fluid consumption.

Rehydration after exercise

After exercise, the goal is to make up any fluid deficit resulting from exercise and to replace electrolytes lost from sweating. How fast to rehydrate depends on when your next training session or competition takes place. If you just ran your first marathon and don’t plan to step foot into those running shoes for at least a few days, then normal meals, snacks, and beverages will generally rehydrate you within about 24 hours.

If you’ve lost excessive fluid (more than 2% of your pre-exercise body weight) and need to be fully recovered in less than 12 hours in order to be ready for another workout or competition, a more aggressive rehydration program is needed. The new ACSM recommendations suggest that you drink about 23 fl oz of fluid for every pound of weight lost during exercise. Drink the necessary fluid gradually between the time you finish your first workout and 1-2 hours before you start your next one.

Also, consuming sodium while rehydrating during recovery will help you retain ingested fluids and help stimulate your thirst. You can get sodium from your recovery beverage, sport drink, energy bar or gel, salty snacks, and meals.

PowerBar tools and products

PowerBar provides easy-to-use tools and state-of-the-art products to meet the individual hydration and fueling needs of athletes:

  • Hydration Calculator: Calculate your sweat rate
  • Recovery Calculator: Get specific hydration and sports nutrition recommendations to promote recovery after a workout or event

For optimal hydration and fueling before, during, and after exercise, you can rely on PowerBar:

  • POWERBAR® Performance bars – each serving provides 41-45 grams of carbs, 8-10 grams of protein, and up to 210 mg of sodium.
  • POWERBAR® Endurance sport drink - each 8 fl oz serving provides 17 grams of carbs and 190 mg of sodium.
  • POWERBAR® Gel - each packet provides 27-28 g of carbs and 200 mg of sodium.
  • POWERBAR® Recovery shake – each 10.6 fl oz ready-to-drink serving provides 34-40 grams of carbs, 13 grams of protein, and 180-220 mg sodium in creamy chocolate and vanilla flavors.
  • POWERBAR® Recovery sport drink- each 16 fl oz serving provides 40 grams of carbs, 6 grams of protein, and 500 mg of sodium in a lighter tasting orange flavor you can chug.


1American College of Sports Medicine; Sawka MN, et al. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc 2007;39:377-390.

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