Carbohydrate Loading?

Carbo-loading? YES, OR NO?

Carbo-loading has been the discussion of many athletes. Some of them swear by it and others say it doesn’t work. But what does the experts say? Everybody knows that muscle glycogen concentration is associated with endurance and performance during training or competing. It is also known that muscle glycogen can be manipulated by your diet. Higher CHO in the diet will give higher muscle glycogen stores, thus will the work capacity improve with a higher CHO diet.

Higher muscle glycogen stores can postpone fatigue by up to 20% in endurance events that last longer than 90 minutes. In events less than 90 minutes glycogen is not really a factor for fatigue. As you should have enough glycogen stores to last you 90 min. It doesn’t really matter if you are carbo-loaded or normal. That does not mean that you can be carbo-depleted.

High CHO diets have been reported to improve TT performance by 2-3%

Up to 75% of your glycogen will come from muscle glycogen. And as the intensity increases so will the total amount of fuel that is being used also increase. The biggest source of fuel is muscle glycogen, but your liver glucose will also increase as intensity increase to supply the muscles with fuel.

Fat oxidation on the other hand will increase from rest to low intensity exercise and it increase further to moderate intensity exercise. But with high intensity exercise the fat oxidation is reduced.

In the picture below you can see that if you start exercise with higher muscle glycogen it has been proven that you can run longer and further than if your glycogen was lower. Also, an interesting observation is that the percentage of walking in the subjects that had less glycogen was more than the subjects with higher glycogen. In the study it was shown that if you start with higher glycogen after the soccer game the glycogen was low but not completely depleted. Whereas the subjects that started with lower glycogen had no glycogen left after the game.

There have been different studies on how to carbo-load. In the study below they took subjects and let them do a hard training session 7 days before an event to completely drain their muscle glycogen levels. Then they followed with a 3-day low carbohydrate diet and then a very high carbohydrate diet for 3 days before the event. The results were that their muscle glycogen was super high the day of the event. The downside to this is that one might not want a very hard training session a week before a big event. In another study training tapering was implemented with a slightly higher carbohydrate diet every day before the event. The day of the event the glycogen was also high. And the strain of hard training a week before was eliminated.

Extremely high glycogen vs slightly lower (but still high) glycogen stores? If you have extremely high glycogen stores the breakdown of glycogen will be much higher. That means after the first 60 minutes of exercise your muscle glycogen might not be that different because you have been breaking it down much faster. After 90-120 minutes there is no difference in super high glycogen stores and high glycogen stores. Up to date there is no studies that show that super high glycogen stores is better than just high glycogen stores.

My advice is to keep your daily intake of carbohydrate higher in training season than it would be in off-season. The timing of your meals is more important than what you eat. Do not confuse carbo-loading with overeating the days before an event. The day before your big event you might even want to eat a little less and eat food that is easy digestible and not heavy on your stomach so that you don’t feel uncomfortable the day of your event. Make sure your post recovery intake of carbohydrate is sufficient for at least the first 4 hours after training to get the glycogen stores restored.

Train Hard but Eat Smart!!!