| A valid connection between hypoglycemia, fatigue and | | | | competition resulted in carbohydrate stores |
| premature termination of exercise been firmly | | | | comparable to those individuals who performed the |
| established and therefore carbohydrate loading is a | | | | glycogen stripping method. In addition, the amount of |
| proven form of boosting running endurance in | | | | training performed before the start of the traditional |
| prolonged events lasting more than two hours in | | | | regime has little effect on the resulting carbohydrate |
| duration. While there are various methods of | | | | stores. Therefore, a well-conditioned athlete may need |
| carbo-loading, the process basically involves consuming | | | | to do little more than consume a higher quantity of |
| large quantities of carbohydrate-rich food in order to | | | | carbohydrates in the three days before competition to |
| saturate the body’s carbohydrate stores. It is | | | | receive full benefit. |
| proposed that with these increased energy stores, the | | | | Optimal carbohydrate loading can be achieved if |
| competitor will be able to avoid exercise-induced | | | | approximately 600g of carbohydrate is consumed |
| hypoglycemia and continue exercising longer than if this | | | | daily for two to three days. It is probably of little matter |
| saturation process had not occurred. This article aims | | | | if the extra carbohydrate is consumed as simple |
| to further explain how to perform carbohydrate loading | | | | (glucose) or complex (starch) carbohydrate. Most |
| and the reasoning behind its practice. | | | | carbohydrates are digested quickly and enter the |
| As previously mentioned in another article on this site | | | | bloodstream via the intestine much the same as if |
| the human body is able to store carbohydrates for | | | | glucose had been ingested. Replenishment rates are |
| energy use in the liver and the muscles in the form of | | | | higher immediately after exercise due to increased |
| a substance known as glycogen. This carbohydrate | | | | insulin sensitivity. The amount ingested should be about |
| store is basically human “starch” and is | | | | 50 to 80g starting immediately after exercise repeated |
| able to be quickly broken down to fuel the muscles | | | | 2 hourly and continuing for the first 6 hours. Full |
| during high intensity exercise (muscle glycogen) and to | | | | glycogen replenishment is usually achieved within 20 |
| maintain blood glucose levels (liver glycogen). In the | | | | hours using this method; however the most rapid |
| unloaded/non-carbohydrate saturated state, an | | | | glycogen resynthesis is observed when glucose is |
| untrained individual consuming an average (45% carb.) | | | | infused directly into the bloodstream, yielding absolute |
| diet is able to store approximately 100 grams of | | | | peak muscle glycogen concentrations of near 800g |
| glycogen in the liver, whereas muscle is able to store | | | | (assuming approximately 20 kg of muscle) within about |
| about 280 grams. Remember also that muscle | | | | 8 hours. Full replenishment of glycogen after an |
| glycogen is committed to be used by muscle and | | | | extended event may take several days longer due to |
| cannot assist in maintaining blood sugar levels. | | | | muscle damage resulting from repeated cycles of |
| Therefore should no additional carbohydrate be | | | | concentric and eccentric contractions. |
| ingested during prolonged exercise, the task of | | | | With the benefits associated with carbohydrate loading |
| maintaining blood glucose levels rests firmly on the | | | | it may be helpful to mention some possible |
| liver’s glycogen stores and gluconeogenesis (the | | | | disadvantages to following this procedure. Firstly, |
| manufacturing of glucose from plasma amino acids). | | | | glycogen storage is associated with a concomitant |
| Oxidation of blood glucose at 70-80% VO2 max is | | | | storage of water. It is estimated that every gram of |
| about 1.0 g/min or about 60 g/hour. Therefore it can be | | | | glycogen stored is associated with about 2.7 grams of |
| predicted that even with full glycogen stores, a less | | | | water. Therefore, a well-conditioned athlete with total |
| conditioned athlete’s liver will be depleted of its | | | | glycogen stores approaching 800g will find their body |
| carbohydrate within and hour and three quarters of | | | | weight about 2kg heavier at the start of the race. This |
| continuous moderate intensity exercise. (Interestingly, | | | | increased body weight will have implications on running |
| the daily carbohydrate requirements of the brain and | | | | economy and performance at least near the beginning |
| nervous system alone are enough to deplete the liver | | | | of the event when energy reserves will be high. As |
| glycogen stores within 24 hours.) Once liver glycogen | | | | the muscles and other organs progressively oxidize |
| levels begin to drop and exercise continues the body | | | | the glycogen stores during exercise, the stored water |
| becomes increasingly hypoglycemic (low blood sugar) | | | | is again released into the body. This may in turn |
| mainly because blood glucose is depleted faster than it | | | | complicate the fluid requirements of the athlete, |
| is replaced by gluconeogenesis. Professor Tim Noakes | | | | requiring them to consume less than a |
| (see profile) considers liver glycogen depletion and | | | | non-carbohydrate loaded competitor. The best advice |
| subsequent hypoglycemia to be the primary factors | | | | for fluid replacement during prolonged exercise may |
| affecting fatigue and performance during extended | | | | be found on this site (see |
| duration races and especially in instances where | | | | How Much Should I Drink? [ and in Lore of Running. A |
| muscle glycogen levels are low as well. | | | | possible solution for water retention and weight gain is |
| The amount of additional carbohydrate that is able to | | | | for the athlete to load to a lesser degree and ingest a |
| be stored in the body is dependent on diet and athlete | | | | carbohydrate/electrolyte enriched drink during exercise |
| conditioning level. For an untrained individual consuming | | | | to help maintain blood glucose and electrolyte balance |
| a high carbohydrate (75%) diet, glycogen stores may | | | | (consuming carbohydrate during an event in the fully |
| increase up to 130 g and 360 g for liver and muscle | | | | loaded state is overkill and produces no additional |
| respectively for a total storage of 490g. For an athlete | | | | benefit). Another drawback to carbohydrate loading if |
| training on a daily basis consuming a normal (45% | | | | performed incorrectly is gastric/intestinal upset. Very |
| carb.) diet, glycogen levels approximate 55 g and 280 | | | | large amounts of ingested carbohydrate can affect |
| g for liver and muscle respectively yielding a total of | | | | the osmolarity of the intestine. In other words, |
| 330 g. However, should this same well-conditioned | | | | carbohydrates (especially simple/processed sugars) in |
| athlete consume a high (75% carb.) diet, their total | | | | the intestine draw water into the gut by osmosis |
| carbohydrate reserves may soar up to 880 g with | | | | affecting the water balance and may cause intestinal |
| approximately 160g stored in the liver and 720 g in the | | | | upset and diarrhea. As mentioned, an athlete should |
| muscle. Clearly the conditioned athlete’s muscles | | | | aim to consume about 600g a day preferably in |
| are much more efficient at storing carbohydrates than | | | | multiple meals/sittings to avoid overloading the digestive |
| those of his or her unconditioned competitor. In | | | | capacities of the body. |
| saturating the muscle by consuming of high levels of | | | | In conclusion, this article has demonstrated the many |
| carbohydrate, the athlete automatically increases their | | | | benefits associated with carbohydrate loading. This |
| time to hypoglycemic fatigue several fold. | | | | process should be viewed as an effective and simple |
| Several methods for carbohydrate loading have been | | | | method for improving performance and endurance |
| described in the literature. The most familiar method is | | | | during extended duration exercise events. Increasing |
| the traditional “glycogen stripping” or | | | | body carbohydrate stores before competition ensures |
| carbohydrate-depletion/carbohydrate loading method. | | | | sufficient energy to avoid hypoglycemic related fatigue |
| This method basically involves the athlete exercising to | | | | and early termination of exercise. Simply consuming |
| exhaustion the sixth day before a major competition | | | | higher quantities of carbohydrate three days before |
| and for the next three days consuming a high | | | | competition may suffice for most athletes, however it |
| protein-fat, low carbohydrate (less than 10% total | | | | is important to follow the loading regimen correctly to |
| energy) diet. On day three the athlete again exercises | | | | avoid intestinal upset. Exercise science is still exploring |
| to exhaustion but for the following three days | | | | the significance and the relative contribution of the two |
| consumes a high (90%) carbohydrate diet. The aim of | | | | sources of glycogen stores to exercise performance |
| this method is to severely deplete the glycogen | | | | and further research will hopefully cast more light on |
| reserves of the body to cause a “super | | | | connections relating to fatigue. |
| compensation” effect in carbohydrate stores. | | | | References and further reading: more information on |
| Research has demonstrated however, that this | | | | carbohydrate loading and a detailed explanation of |
| glycogen stripping method may not in fact be | | | | carbohydrate contributions during exercise can be |
| necessary to achieve optimal carbohydrate saturation | | | | found in Lore of Running – a classic book in its |
| in well-trained individuals and that this super | | | | fourth edition dedicated not only to running |
| compensation effect may not even occur. Studies | | | | performance, but to cutting edge exercise physiology |
| have demonstrated that athletes simply consuming a | | | | as well. |
| high (75%) carbohydrate diet for three days prior to | | | | |