Training Dictionary
Carbohydrates
Definition: Carbohydrates can be found as either simple sugars (mono-saccharide or di-saccharide), as a starch (long branched chain from plant source), glycogen (long branched chain from meat source), or fiber (not an energy source for humans). Carbohydrates are made from Carbon, Hydrogen, and Oxygen.1
Carbohydrates are primarily burned from the stored form known as glycogen in the liver and skeletal muscles (muscles aside from the heart and organs). Glycogen is a long branched chain built from glucose molecules. When exercising, working muscles will break down glycogen as fuel for energy production. When glycogen supplies are depleted, a rider will often feel what is known as "bonking".2
After successive days of hard training, the bodies available glycogen supplies become depleted. This depletion will lead to diminished exercise performance.3 To prevent this from occurring, rest days are given to literally, refuel. It is also important to keep glycogen supplies protected during your ride and replenished after your ride. This means consuming carbohydrates during exercise and consuming ample carbohydrates directly after a ride.4
Effects of Exercise
Carbohydrates are a quick energy source. Skeletal muscles and the liver act as a fuel tank to provide glycogen as a steady, quick carbohydrate source. Exercising can increase fat metabolism, which helps spare glycogen supplies.
Exercise can also increase glycogen storage capacity, especially with anaerobic training. This means that you will be able to exercise at a higher intensity for a greater duration. With an increased supply of glycogen you will also have a greater capacity to burn energy quicker. In all, this means that you will be able to perform at a high intensities for a longer duration (it is like adding another wick in a large candle to produce a more intense flame).
Important Details
Your primary source of fuel during exercise should always be carbohydrates.
Sources:
1 Campbell, N. A., Reece, J. B., L. G. Mitchell 1999. Biology. 5th Edition. Addison Wesley Longman, Glenview, IL: 61-64 pp.
2 Baldwin, K. M. et al. Depletion of muscle and liver glycogen during exercise. Pflügers Archiv European Journal of Physiology 1975: 354:3 203-212.
3 E. R. Chin & D. G. Allen. Effects of reduced muscle glycogen concentration on force, Ca2+ release and contractile protein function in intact mouse skeletal muscle. The Journal of Physiology 1997: 498, 17-29.
4 McArdle, Katch, F. I., & V. L. Katch, 2001. Exercise Physiology: Energy, Nutrition, and Human Performance. 5th Edition. Lippincott Williams & Wilkins, Philadelphia: 85, 92-93 pp.
