Endurance athletes burn a combination of fat and carbohydrates as fuel during exercise. The harder you're working, the more you're relying on carbs as fuel. The problem is that while fat stores are virtually endless, precious carb reserves in the form of glycogen in the liver and muscles, and glucose in the bloodstream, can be depleted in just a few hours. Once that occurs, fatigue sets in and your performance falls off dramatically. This is bad news for all those athletes out there running marathons, competing in triathlons, racing bikes, or involved in other endurance challenges.
Researchers in exercise performance laboratories worldwide have long searched for ways to make carbohydrate reserves last longer. They've tried pushing athletes to consume more carbs during exercise in an effort to spare their existing stores. But no matter how much they're fed, study after study found that athletes weren't able to effectively utilize more than about 60 grams of ingested carbohydrates per hour of exercise, or about 1 gram every minute. Moreover, the extra unabsorbed carbs would just build up in the gastrointestinal tract, causing fluids to be sucked into the gut. Bloated and with fluid jostling about uncomfortably, athletes ended up nauseous instead of energized.
Breaking Through the Energy Ceiling
The 1-gram-per-minute energy ceiling seemed insurmountable, but researchers went back to the drawing board. One group hit on the idea of using different carbohydrate sources instead of what at the time was considered the gold standard — glucose alone.(1) The idea was inspired by the fact that scientists had discovered that some carbohydrates, such as glucose, have a specific transport system in the gut that is entirely devoted to promoting the absorption of that specific sugar. What the researchers hadn't appreciated was the fact that these special transporters become saturated if too much glucose is fed. Much like a train with no more available seats, the glucose transporters could only carry to their capacity. Any extra glucose, like stranded passengers left standing at the train station, remained behind in the digestive tract. Intrigued by this new idea, researchers speculated that if they fed different carbohydrates — each one with its own dedicated transport system — they might be able to break through that energy ceiling and deliver more carb fuel to working muscles.
Incredibly, the idea worked. The researchers selected two different carbohydrates — glucose and fructose — as each one has their own unique and separate transport system. Feeding a 2:1 ratio of glucose and fructose, the investigators were able to break through that seemingly impenetrable energy ceiling. Instead of utilizing just 1 gram of ingested carbohydrate every minute during exercise, they were able to boost the carbohydrate fuel usage rate of the athletes by another 50% on average!
Theory Put to the Test
While excited by their findings, naturally skeptical researchers set about to determine whether delivering more carbohydrate muscle fuel to athletes would actually result in better endurance performance.
To answer the question, they set up a laboratory simulation of an ultra-endurance event. Eight well-trained cyclists were asked to pedal at a steady, vigorous pace over a period of 5 hours while consuming beverages containing either glucose alone, glucose and fructose in a 2:1 ratio, or plain water. Just as predicted, ingestion of what scientists were now calling transportable carbohydrates — a combination of glucose and fructose — resulted in significantly greater utilization of ingested carbs as muscle fuel in comparison to glucose alone.
The study also provided the very first indication of improved performance. During the 5-hour endurance test, cyclists were asked to rate how hard they felt they were working. Investigators call this perceived exertion, and it was lowest among athletes consuming the glucose-fructose mixture. As a testament to the difficulty of the exercise, when plain water alone was administered to the athletes, not all were able to complete the arduous 5-hour ride.
Perceived exertion is just part of the performance story. A decline in pedal cadence during a test such as this is generally acknowledged as an indication of developing fatigue. Cyclists who drank only plain water had the lowest cadence during the last hour of the ride. Those who drank the glucose beverage started strong at 89 rpm in the first hour, but limped in at only 78 rpm in the final hour. But with the glucose and fructose combination, pedal cadence was the highest, almost unchanged over the 5-hour test. This was proof positive that not only had the carb fueling ceiling been broken, the extra carbs were generating a measurable performance benefit.
But what about during a shorter-duration endurance test — something akin to a time trial? Would the glucose-fructose carbohydrate combination make a difference in that setting?
That piece of the scientific puzzle was just recently published. As a follow-up to the earlier study, researchers again selected eight well-trained endurance cyclists, but this time they had them pedal at a steady, vigorous pace for 2 hours, and then perform a time trial designed to last an additional 60 minutes. While riding, the cyclists were given identical-looking and -tasting beverages that contained either glucose alone, a combination of glucose and fructose in a 2:1 ratio, or plain water. To judge endurance performance, the power output of the athletes over the last hour was measured. Lower power is associated with greater fatigue. Just as predicted, athletes consuming the glucose-fructose combination had a formidable 8% improvement in time-trial performance compared to when glucose alone was consumed, and a an even greater improvement in comparison to when plain water was fed.
Collectively these data led to two very clear conclusions about performance during endurance exercise:
- Carbohydrates absolutely outperform no carbs
- Transportable carbohydrates — a combination of glucose and fructose — outperform glucose alone, which to that point had been considered the gold-standard fuel
New Benefits of Transportable Carbohydrates Emerge
May Enhance Fluid Delivery
A concern about consuming concentrated carbohydrate beverages during exercise is that they can actually slow down the rate at which fluids are released from the stomach, and that this will impair fluid absorption. However, evidence suggests that impaired fluid delivery may actually be minimized when transportable carbs are in the mix. In fact, researchers prepared and administered two different 15% carbohydrate solutions. One had glucose alone while the other had a combination of glucose and fructose. Typically, highly concentrated solutions like this would severely impair fluid delivery. However, researchers found that gastric emptying and fluid delivery to the bloodstream were significantly better with the glucose-fructose combination compared to glucose alone.
Beating the Heat
One of the toughest tests for endurance athletes is training or competing in the heat. A contributing factor to the difficulty is the fact that glycogen stores, rather than ingested carbs, are preferentially used during exercise. This leads to faster depletion of glycogen reserves and earlier onset of fatigue when exercising in high temperatures. Also, greater fluid losses from sweating increase the risk of dehydration, which in turn impairs the ability to perform. To evaluate the impact of transportable carbohydrates during exercise in the heat, researchers had well-trained athletes cycle in 90° heat over a 2-hour period while drinking a beverage containing glucose alone or the combination of glucose and fructose in a 2:1 ratio. Despite the debilitating heat, the carbohydrate combination resulted in a higher utilization of ingested carbs as muscle fuel in comparison to the beverage containing glucose alone. In addition, the beverage with the blend of carbs also proved to be more effective at replacing fluids lost during exercise.
Thus, through an ever-growing list of published studies, researchers have made a compelling case for transportable carbohydrates as the fuel of choice during endurance exercise. Benefits in comparison to glucose alone include:
- Increased delivery of carbohydrate fuel to working muscles
- Enhanced emptying of fluids from the gut and improved delivery of fluids to the bloodstream
- Better reliance on ingested carbs as fuel in difficult, high-temperature conditions
- Increased endurance performance
Do Performance Benefits Extend to Bars and Gels?
While the list of advantages was impressive, all these benefits were seen when the 2:1 ratio of glucose to fructose was administered in beverage form, essentially a sports drink. What remained a question mark was whether the benefit would extend to solid carbohydrate sources taken during exercise, such as bars and gels?
This question was critical because while a sports drink is a mainstay of the sports nutrition arsenal for many endurance athletes, during prolonged exercise, bars and gels are also frequently used to meet carbohydrate fuel needs.
In two studies recently presented at large, prestigious scientific meetings, this important question was answered.
In one study, researchers had eight well-trained cyclists and triathletes pedal for three hours at a steady and vigorous pace. During the test, they consumed either plain water, a carbohydrate bar plus water, or a carbohydrate beverage. Researchers measured how well the ingested carbs were utilized as muscle fuel — they found virtually no difference between the carbs delivered in solid form versus those delivered in liquid form. In addition, blood glucose and insulin levels were comparable throughout the trial, which is further affirmation of the similarity between solid and liquid delivery.
A virtually identical trial was conducted with transportable carbohydrates delivered in gel form versus liquid form. Here again, there was essentially no difference in the carbohydrate burn rate when comparing the gel and beverage versions.
The investigators in these studies concluded that whether the 2:1 glucose-to-fructose ratio is delivered as a beverage, a bar, or a gel, in all cases the rate of utilization of the ingested carbs as muscle fuel was well beyond the 1-gram-per-minute rate, and there was virtually no difference in the muscle fueling effectiveness between the different forms.
Research Translated into Practice
This groundbreaking research on transportable carbohydrates is the basis for the muscle fueling innovation known as PowerBar
® C2MAX dual source energy blend. Seeing the incredible performance potential in this cutting-edge research, and in collaborating with the researchers pioneering this scientific work, PowerBar
® scientists have incorporated the 2:1 ratio of glucose and fructose into each and every PowerBar sports nutrition product intended to fuel and hydrate athletes during exercise. PowerBar C2MAX dual source energy blend can be found in PowerBar Ironman PERFORM™ sports drink,
PowerBar® Energy Gel,
PowerBar® Sport Energy™ bar,
PowerBar® Fruit Energize™ bar,
PowerBar® Energy Bites™, and
PowerBar® Gel Blasts™ Energy chews. If it's designed to be taken during high intensity exercise and it's made by PowerBar, you can be sure it's powered by C2MAX.
The adage of no more than 60 grams of carbs per hour during exercise is now old school. The 2:1 glucose-fructose blend has been shown to be utilized at up to 90 grams per hour. Thus, usage recommendations for serious training and competing can be increased. If you're using PowerBar products with C2MAX, you can take in up to 90 grams of carbs per hour.
References:
Currel K, Jeukendrup AE. Superior endurance performance with ingestion of multiple transportable carbohydrates. Med Sci Sports Exerc 2008; 40:275–281.
Jeukendrup AE, Mosely L. Multiple Transportable Carbohydrates Enhance Gastric Emptying and Fluid Delivery. Scand J Med Sci Sports 2008.
Pfeiffer B, Stellingwerff T, Zaltas E, Jeukendrup AE. Oxidation of Solid versus Liquid Carbohydrate Sources during Exercise. Med Sci Sports Exerc. 2010 Mar 19. [Epub ahead of print].
Pfeiffer B, Stellingwerff T, Zaltas E, Jeukendrup AE. Carbohydrate Oxidation from a Carbohydrate Gel Compared To a Drink during Exercise. Med Sci Sports Exerc. 2010 Apr 16. [Epub ahead of print].
Jeukendrup AE, Pfeiffer B, Zaltas, E, Stellingwerff T. Carbohydrate Oxidation from a Carbohydrate Gel Compared to a Drink During Exercise. Abstract presented at…
Topics:
C2MAX, Energy, Research, Muscle
Rights of Usage Policy