Science of Sports Drinks - Electrolytes, Hydration, Isotonic and Hypertonic Drinks

Science of Sports Drinks - Electrolytes, Hydration, Isotonic and Hypertonic Drinks

Even as little as a 2% loss in hydration can lead to significant declines in performance and focus while also increasing the risk of injury. [1]

Statistics like these have helped to build the sports drinks market into a multi-billion dollar a year industry.

And, while sports drinks seem ubiquitous, there was a time not so long ago when they weren’t so commonplace.

Related - Do You Need Electrolytes?

In this article, we’ll discuss the history of sports drinks, the various types of sports drinks you’ll find on the market, and why the most popular sports drinks available might not be your best option for rapidly rehydrating.

Origins of Sports Drinks

Believe it or not, Gatorade was not the first sports drink to land on the scene. That honor belongs to another ade which interestingly enough also began with a “G.”

The drink was called Glucozade, and it was developed by chemist William Owen in 1927 as a way to deliver readily-digestible energy and fluids quickly to anyone who was ill.

If that name sounds vaguely familiar, it’s because we’ve covered it before when discussing the history of energy drinks.

As you might imagine, product flavoring wasn’t quite what it is today (it wasn’t even in the same galaxy). As such, Glucozade tasted pretty bad by today’s standards as it was essentially citrus-flavored sugar water.

Glucozade was later renamed to the shorter Lucozade and enjoyed a good bit of success, so much so that the Beecham Company acquired the brand from Owen in 1938.

Thanks to some clever marketing campaigns, Lucozade was very lucrative, and by the 1950s accounted for 50+% of the Beecham Company’s profits.

However, Lucozade’s success wasn’t on account of its popularity with athletes (it wasn’t really advertised as a “sports” product until the late 1980s). It was predominantly used as a medicinal product and contained significantly more sugar than its would-be successor as well as little-to-no salt.

Then, in 1965, sports nutrition changed forever when a group of researchers from the University of Florida College of Medicine created Gatorade. [2]

The physician’s name who was leading the charge for the product’s development interestingly enough rhymes with Gatorade -- Dr. Robert Cade.

Cade was a kidney specialist who was recruited by then Gator coach, Dwayne Douglas, to find out why the football players were losing a significant amount of weight during training and games despite drinking water.

Even more alarming was the fact that the players weren't urinating and some were even suffering from heatstroke.

To solve these problems, Cade and his team set out to develop a beverage that would actually hydrate the players since plain water wasn’t doing the trick. The end result of their toils was a drink that contained a fair amount of salt and water with some sugar mixed into it.

As you can imagine, this hydration-boosting concoction didn’t taste all that great, but it sure worked.

To help make the drink more palatable for the players, Dr. Cade’s wife suggested that they add lemon juice to the mixture, which apparently worked, and in the summer of 1966, the Florida Gators football team started chugging Gator-ade and noticed a significant decrease in the players suffering from heat exhaustion as well as those losing significant amounts of weight.

In the fall of 1967, Stokely-Van Camp Co. took the reigns of distribution and held it for over 15 years. Then, in 1983, Quaker Oat acquired distribution rights which stood in place until 2001, when Quaker Oats was bought by Pepsi Co.

And, as usual when a product enjoys immeasurable success and meteoric rise, imitators will follow, and there is certainly no shortage of available sports drinks options today. A few of the more notable competitors (imitators) are:

  • Powerade
  • 10-K (a childhood favorite of yours truly)
  • Staminade
  • BodyArmour SuperDrink
  • Accelerade

While each of these drinks might appear to be the same based off of a cursory glance, subtle differences do exist, which brings us to our next section in all things sports drinks...

Different Types of Sports Drinks

Sports drinks can be categorized by their tonicity.

What is Tonicity?

Tonicity of a drink is a measure of the relative concentration of sugars and salts compared with the concentration of those compounds found in the blood. You can essentially think of tonicity as the “thickness” of a given solution.

The difference between the two (the beverage and your blood) dictates the amount and the direction of fluid absorption following ingestion of the beverage.

A less tonic solution will be more readily absorbed than one of equal tonicity or greater tonicity. This is primarily due to the principle of osmosis, which is the net movement of solvent molecules through a selectively permeable membrane, which in our case is the drink and your blood.

The “selectively permeable membrane” is the lining of your gut as well as the cellular membrane (which serves as the barrier between molecules in the blood and molecules within the cell).


Far and away the most common type of sports drinks are isotonic, meaning that they are of similar concentration to blood.

FYI, human blood has a concentration of ~285 to 295mOsm/kg.

Isotonic drinks generally contain between 6-8% carbohydrates and supply athletes with roughly similar amounts of energy (carbs), electrolytes (sodium, potassium), and fluids.

Interestingly, while most conventional sports drinks are marketed as being isotonic, a 2006 review found the drinks to be slightly hypertonic, meaning they are more concentrated than the blood. [3,4]

Gatorade, for instance, was found to have tonicity of 350mmol/kg while its inferior-tasting brethren (Powerade) had a concentration of 391 mmol/kg.

Why is this noteworthy?

Well, hypertonic solutions digest more slowly, which means they’re not ideal for rehydrating. As such, it’s not entirely uncommon for higher-level athletes to dilute (water down) commercial sports drinks to make them hypotonic, less concentrated than the blood.

And to further compound the problem, this delayed gastric emptying caused by the hypertonicity, can lead to GI distress and the ever-so-pleasant feeling of liquid “sloshing” around your gut while your training.

As a result, isotonic drinks which are more likely to actually be hypertonic based on the research) are best reserved for those engaging in short bouts of high-intensity training where energy is in higher demand than hydration.

In the end, isotonic drinks strike a balance between hydration and energy repletion, they’re kind of a jack of all trades, but don’t really excel at either category.


As we just discussed, hypertonic drinks are more concentrated than the blood, typically containing around 10% carbohydrate composition.

The focus or purpose of hypertonic drinks is to supply the athlete with a rapid infusion of energy rather than restore lost hydration, making them ideally suited for the post-workout period when the athlete is concerned with replenishing muscle glycogen as fast as possible ahead of an upcoming bout of training or competition.

So, why are hypertonic drinks less than ideal when hydration is the focus of drinking a sports drink?

When a hypertonic drink arrives in your gut, after passing through the stomach, the concentration of the fluid in your intestines becomes hypertonic. As a result, your body then has to do some “rearranging” by first moving water out of the bloodstream and into the intestine to dilute the concentration of the fluid in your gut, thereby creating the proper gradient to allow for diffusion of the ions across the gut wall into the blood.

During this phase when water is moving out of the blood and into the gut, you’re technically becoming dehydrated (albeit briefly).

And therein lies the problem with hypertonic drinks when it comes to endurance-style training, the priority is on hydration, not energy delivery. As a result, you might feel more thirsty for a time as well as a bit queasy -- neither of which you want to happen during an endurance event.

Again, these drinks are best reserved for those athletes engaged in short-duration activities or as a post-workout drink, not those engaged in long-duration activities, like running a 50k hiking venture or competing in a triathlon.


If long-duration events are your jam, then hypotonic drinks are your go-to sports drink.

As the name implies, hypotonic drinks are less concentrated than the blood, which facilitates faster digestion, uptake, and transference of vital electrolytes to the blood than isotonic drinks due to a favorable osmotic gradient. [4]

Typically, hypotonic sports drinks contain less than 6% carbohydrate content.

As such, hypotonic drinks are great for restoring hydration, but not ideal when seeking to get some energy quickly. This makes them ideal for endurance-style training, but not so much for short, high-intensity activities where energy is at a premium.

Sports Drink Summary

  • Sports drinks are not the same as energy drinks. The purpose of an energy drink is to boost energy (usually in the form of sugar and caffeine). The purpose of sports drinks is to replenish minerals, fluids, and energy with the goal being to enhance performance.
  • The concentration of the sports drink ultimately determines how it performs and for what application it is best suited.
  • Isotonic drinks = same concentration as blood, does a decent job of replenishing hydration and energy
  • Hypertonic drinks = more concentrated than blood, good for energy delivery, poor for hydration and endurance training due to the delayed gastric emptying and temporary dehydration that occurs
  • Hypotonic drinks = less concentrated than blood which makes for the fastest transfer of fluids and minerals, good for fluid replenishment, electrolyte delivery, and endurance training, bad for energy delivery.

The Next Era of Hydration

As you can see, there really isn’t a “one size fits all” approach when it comes to sports drinks. Even if you purchase the right style of drink for your particular type of training, that’s not necessarily a guarantee it will work as well as it should.

Sure, it may get the job done, but it might not be “optimal.”

The reason for this boils down to inter-individual differences. Every person will have a different rate of electrolyte usage and loss as well as water loss through sweat.

This is why it’s not possible to create a fluid replacement procedure for everyone that covers every situation.

And, with the increased fear of all things carbohydrates (even amongst certain professional athletes) and “chemicals”, sports drinks manufacturers have begun focusing more and more on hydration (hypotonic drinks) as well as ones that contain only “natural ingredients”, such as stevia, monk fruit extract, or cane sugar.

Hell, even the industry leader, Gatorade, has had to adapt to the changing tide and it launched an “organic” line of sports drinks, in G Organic.

Other recent innovations in the sports drink market include that replacement of fast-digesting carbohydrates like glucose, maltodextrin, etc. with slow-digesting carbs that won’t spike blood sugar and provide a more sustained release of energy for athletes. These slower digesting carbohydrates might be a better fit for hypotonic solutions where the focus isn’t on energy, but hydration.

Do I Even Need a Sports Drink?

Likely not.

If you’re not exercising all that hard or for a very long time (75+ minutes), then you don’t need a sports drink.

Your pre-workout meal should likely take care of your nutrient needs for the upcoming workout.

However, if you’re participating in multiple rounds of training or competition in a single day or performing one long-duration event, then it’s probably a good idea to use some kind of sports drink.

And when you are searching for a sports drink, here are a few helpful tips:

First, make sure to choose the type of drink that’s best suited to your particular athletic event -- hypotonic (hydration) or hypertonic (energy).

For electrolytes, a good choice is sodium citrate or potassium citrate. Citrates tend to be easier on the gut and increase the absorption of fluids, promoting greater hydration.

For carbohydrates, look for a mix of carbohydrates as different carb sources utilize different pathways through the intestinal wall, increasing the rate and amount of absorption (and thereby energy repletion).


1) Backes TP, Fitzgerald K. Fluid consumption, exercise, and cognitive performance. Biol Sport. 2016;33(3):291–296. doi:10.5604/20831862.1208485

2) Gatorade: The Idea that Launched an Industry. (n.d.). Retrieved from

3) Mettler, S., Rusch, C., & Colombani, P. (2006). Osmolality and pH of sport and other drinks available in Switzerland. Schweizerische Zeitschrift fur Sportmedizin und Sporttraumatologie(Vol. 54).

4) Rowlands, D. S., Bonetti, D. L., & Hopkins, W. G. (2011). Unilateral fluid absorption and effects on peak power after ingestion of commercially available hypotonic, isotonic, and hypertonic sports drinks. International Journal of Sport Nutrition and Exercise Metabolism, 21(6), 480–491.

5) Ward, Luke. "The History of Lucozade." The Fact Site. March 2009. (Feb. 27, 2013)

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