|The Lounge | Champions | The Wire | Schedule | Audio | Arcade | The Top Ten | Historical | Email | Video|
The Science of Carbohydrate Loading
A valid connection between hypoglycemia, fatigue and premature termination of exercise been firmly established and therefore carbohydrate loading is a proven form of boosting running endurance in prolonged events lasting more than two hours in duration. While there are various methods of carbo-loading, the process basically involves consuming large quantities of carbohydrate-rich food in order to saturate the body's carbohydrate stores. It is proposed that with these increased energy stores, the competitor will be able to avoid exercise-induced hypoglycemia and continue exercising longer than if this saturation process had not occurred. This article aims to further explain how to perform carbohydrate loading and the reasoning behind its practice.
As previously mentioned in another article on this site the human body is able to store carbohydrates for energy use in the liver and the muscles in the form of a substance known as glycogen. This carbohydrate store is basically human "starch" and is able to be quickly broken down to fuel the muscles during high intensity exercise (muscle glycogen) and to maintain blood glucose levels (liver glycogen). In the unloaded/non-carbohydrate saturated state, an untrained individual consuming an average (45% carb.) diet is able to store approximately 100 grams of glycogen in the liver, whereas muscle is able to store about 280 grams. Remember also that muscle glycogen is committed to be used by muscle and cannot assist in maintaining blood sugar levels. Therefore should no additional carbohydrate be ingested during prolonged exercise, the task of maintaining blood glucose levels rests firmly on the liver's glycogen stores and gluconeogenesis (the manufacturing of glucose from plasma amino acids). Oxidation of blood glucose at 70-80% VO2 max is about 1.0 g/min or about 60 g/hour. Therefore it can be predicted that even with full glycogen stores, a less conditioned athlete's liver will be depleted of its carbohydrate within and hour and three quarters of continuous moderate intensity exercise. (Interestingly, the daily carbohydrate requirements of the brain and nervous system alone are enough to deplete the liver glycogen stores within 24 hours.) Once liver glycogen levels begin to drop and exercise continues the body becomes increasingly hypoglycemic (low blood sugar) mainly because blood glucose is depleted faster than it is replaced by gluconeogenesis. Professor Tim Noakes (see profile) considers liver glycogen depletion and subsequent hypoglycemia to be the primary factors affecting fatigue and performance during extended duration races and especially in instances where muscle glycogen levels are low as well.
The amount of additional carbohydrate that is able to be stored in the body is dependent on diet and athlete conditioning level. For an untrained individual consuming a high carbohydrate (75%) diet, glycogen stores may increase up to 130 g and 360 g for liver and muscle respectively for a total storage of 490g. For an athlete training on a daily basis consuming a normal (45% carb.) diet, glycogen levels approximate 55 g and 280 g for liver and muscle respectively yielding a total of 330 g. However, should this same well-conditioned athlete consume a high (75% carb.) diet, their total carbohydrate reserves may soar up to 880 g with approximately 160g stored in the liver and 720 g in the muscle. Clearly the conditioned athlete's muscles are much more efficient at storing carbohydrates than those of his or her unconditioned competitor. In saturating the muscle by consuming of high levels of carbohydrate, the athlete automatically increases their time to hypoglycemic fatigue several fold.
Several methods for carbohydrate loading have been described in the literature. The most familiar method is the traditional "glycogen stripping" or carbohydrate-depletion/carbohydrate loading method. This method basically involves the athlete exercising to exhaustion the sixth day before a major competition and for the next three days consuming a high protein-fat, low carbohydrate (less than 10% total energy) diet. On day three the athlete again exercises to exhaustion but for the following three days consumes a high (90%) carbohydrate diet. The aim of this method is to severely deplete the glycogen reserves of the body to cause a "super compensation" effect in carbohydrate stores. Research has demonstrated however, that this glycogen stripping method may not in fact be necessary to achieve optimal carbohydrate saturation in well-trained individuals and that this super compensation effect may not even occur. Studies have demonstrated that athletes simply consuming a high (75%) carbohydrate diet for three days prior to competition resulted in carbohydrate stores comparable to those individuals who performed the glycogen stripping method. In addition, the amount of training performed before the start of the traditional regime has little effect on the resulting carbohydrate stores. Therefore, a well-conditioned athlete may need to do little more than consume a higher quantity of carbohydrates in the three days before competition to receive full benefit.
Optimal carbohydrate loading can be achieved if approximately 600g of carbohydrate is consumed daily for two to three days. It is probably of little matter if the extra carbohydrate is consumed as simple (glucose) or complex (starch) carbohydrate. Most carbohydrates are digested quickly and enter the bloodstream via the intestine much the same as if glucose had been ingested. Replenishment rates are higher immediately after exercise due to increased insulin sensitivity. The amount ingested should be about 50 to 80g starting immediately after exercise repeated 2 hourly and continuing for the first 6 hours. Full glycogen replenishment is usually achieved within 20 hours using this method; however the most rapid glycogen resynthesis is observed when glucose is infused directly into the bloodstream, yielding absolute peak muscle glycogen concentrations of near 800g (assuming approximately 20 kg of muscle) within about 8 hours. Full replenishment of glycogen after an extended event may take several days longer due to muscle damage resulting from repeated cycles of concentric and eccentric contractions.
With the benefits associated with carbohydrate loading it may be helpful to mention some possible disadvantages to following this procedure. Firstly, glycogen storage is associated with a concomitant storage of water. It is estimated that every gram of glycogen stored is associated with about 2.7 grams of water. Therefore, a well-conditioned athlete with total glycogen stores approaching 800g will find their body weight about 2kg heavier at the start of the race. This increased body weight will have implications on running economy and performance at least near the beginning of the event when energy reserves will be high. As the muscles and other organs progressively oxidize the glycogen stores during exercise, the stored water is again released into the body. This may in turn complicate the fluid requirements of the athlete, requiring them to consume less than a non-carbohydrate loaded competitor. The best advice for fluid replacement during prolonged exercise may be found on this site (see How Much Should I Drink? ) and in Lore of Running. A possible solution for water retention and weight gain is for the athlete to load to a lesser degree and ingest a carbohydrate/electrolyte enriched drink during exercise to help maintain blood glucose and electrolyte balance (consuming carbohydrate during an event in the fully loaded state is overkill and produces no additional benefit). Another drawback to carbohydrate loading if performed incorrectly is gastric/intestinal upset. Very large amounts of ingested carbohydrate can affect the osmolarity of the intestine. In other words, carbohydrates (especially simple/processed sugars) in the intestine draw water into the gut by osmosis affecting the water balance and may cause intestinal upset and diarrhea. As mentioned, an athlete should aim to consume about 600g a day preferably in multiple meals/sittings to avoid overloading the digestive capacities of the body.
In conclusion, this article has demonstrated the many benefits associated with carbohydrate loading. This process should be viewed as an effective and simple method for improving performance and endurance during extended duration exercise events. Increasing body carbohydrate stores before competition ensures sufficient energy to avoid hypoglycemic related fatigue and early termination of exercise. Simply consuming higher quantities of carbohydrate three days before competition may suffice for most athletes, however it is important to follow the loading regimen correctly to avoid intestinal upset. Exercise science is still exploring the significance and the relative contribution of the two sources of glycogen stores to exercise performance and further research will hopefully cast more light on connections relating to fatigue.
References and further reading: more information on carbohydrate loading and a detailed explanation of carbohydrate contributions during exercise can be found in Lore of Running - a classic book in its fourth edition dedicated not only to running performance, but to cutting edge exercise physiology as well.
David Petersen is an Exercise Physiologist/Certified Strength and Conditioning Specialist and the owner and founder of B.O.S.S. Fitness Inc. based in Oldsmar, Florida. More articles and information can be found at http://www.bossfitness.com
NOTE: You're free to republish this article on your website, in your newsletter, in your e-book or in other publications provided the article is reproduced in its entirety, including the author information and all LIVE website links as above.
Exercising With Kids -- Tips For Parents
Making exercise a priority is a challenge for everyone. And for parents it can be especially difficult to find time to workout because of the full plates that they often juggle.
Exercise - More is NOT Better!
Years ago when I was a professional bodybuilder, I fell into the mindset that the more I exercised, the less fat I ate, the better I would look and feel. At the time this seemed like the logical thing to do.
Stay Mentally Focused When Training
When you decide to exercise, try to really stick to your training routine and don't get sidetracked by too much socializing. When you socialize with friends, your mind usually starts to wander off and you really start to lose focus on your main objective, which is to train hard and get out of there.
Fitness the Goddess Way: Movement vs. Exercise
I was excited to hear the esteemed speakers at the Fall 2004 Omega Institute Conference. The "biggies" of the women's movement such as Gloria Steinem, today's best-selling authors and who's who of empowering women doing inspiring work were.
The Top 10 Reasons Why Your Dog is a Great Workout Partner
1) He or she is never late for a workout session. Chances are good that your dog lives with you and has a reasonable clear schedule.
Top 10 Mistakes To Avoid When Exercising the Abdominals
The abdominal muscles are essential for maintaining good posture and core stability, however many exercisers are unclear on the correct way to exercise them. Traditional exercises for the abdominals include crunches and sit-ups also known as trunk curls and curl-ups.
Exercising for life - The magic is in the synergy!
Synergy: the working together of two or more things, people,or organizations, especially when the result is greater thanthe sum of their individual effects or capabilitiesMomentum toward your goals is generated when all componentsof fitness are incorporated into your workout program." Heart-through cardiovascular workout" Skeletal muscle-through strength training" Joints-through flexibility exercises.
Professional Triathlon Training Taking You To Your Best
There are hundreds of different programs for professional triathlon training that will work for you. There are even more that won't.
Incorporating Physical Activity into Your Daily Routine Not as Hard as You Think
You already know that getting at least 30 minutes of exercise each and every day is good for you, but putting that assertion into actual practice is an entirely different matter, right? Contrary to what you might think, making physical activity an everyday habit isn't rocket science. There's no secret code for success waiting to be cracked.
Life Walking: Dont Walk Just For Exercise - Change Your Life
"Life walking" is more than walking for exercise and fitness objectives. It's the larger ideal of using walking to change your life.
Super Secret Exercise Tips for People with Arthritis
People with arthritis should exercise ? but they need to keep some valuable information in mind. Here are some important tips to follow:1.
Do You Have A Fitness Battle Plan?
In fitness, as in war, you want to be on the offensive, not the defensive and this means that rather than reacting to maladies as they occur, far better to be in good general physical condition; preventive maintenance is preferable to remedial effort every time. One general rule of thumb I use is energy is the basic coin of the fitness realm and without it is damned difficult to mount any kind of serious fitness effort.
When Exercising Right Looks Wrong II
Enter any health club and a concept is very apparent, the same exercise performed again and again. Crowded floor space taken up by machines designed to make exercise easier, and a thought process called 'gym science' which involves no science at all.
Stretching and the Warm up - Are You Confused?
Lately, I've been receiving a lot of questions referring to the latest studies and research findings, and one question that I receive most queries about concerns the role that stretching plays as part of the warm up.Currently, there seems to be a lot of confusion about how and when stretching should be used as part of the warm up, and some people are under the impression that stretching should be avoided altogether.
Physical Fitness - Is Your Workout Missing Something?
Hiking along a rocky trail, two of the three friends carefully picked their way from rock to rock. But one leaped from rock to rock, bounding by the others like a gazelle running and leaping from rock to rock.
Doing vs. Performing: The Difference Between Exercising and Getting Results
Back when I was young and living on my parents' farm, there always seemed to be plenty of tasks that were reserved for the low man on the totem pole. And you guessed it.
Top 3 Back Pain Risk Factors
Lower back pain is an increasingly common problem in fact four out of five Americans will experience lower back pain at least once in their lifetime.Properly training the lower back involves selecting the right exercises to work this area and using good technique to make sure that you are getting the most out of the movement.
Exercise and Kids: The Difference between Training Children and Adults!
The greatest mistake a person can make when exercising with children is to treat them like little adults. Children are growing and developing rapidly.
Success Versus Failure in the Exercise Department
Success is what you are prepared to make of yourself every single day. That one cold morning when you want to roll over but instead get up and go to workout, is a defining moment.
Lose Weight - Stay Fit and Stick With It!
Health and nutrition experts continually advise us that the more we exercise the healthier we will be. In magazines, the doctor's office or on television we are never far from information showing us how to exercise, what to eat and how to lose weight.
Section Site Map - Submit News - Feedback - Comments - Advertise with Us
Copyright © 2006 Luminati Inc. All rights reserved.