General Characteristics

• polysaccharide, (C-6, H-10, O-5)n
• stored primarily in the liver and muscle tissue
• readily converted to glucose as needed by the body to satisfy its energy needs
• supplies energy during heavy work.
• stored with water (1 gram of carbohydrates stored with 3 grams of water)
• central nervous system (CNS) is dependent on hepatic glycogen for energy

Glycogen vs Fat

• Glycogen can be rapidly mobilized in skeletal muscle
• Glycogen can be utilized a fuel substrate in the absence of oxygen
• Fat oxidation requires energy input
• Glycogen can maintain blood glucose levels to be used by certain tissues such as the brain
  • Carbon atoms of fat cannot be used by any pathway of the body
• Glycogen stores significantly more limited than adipose tissue

Effects on Performance

• Increased storage can double duration of exhaustive work
• Low or depleted glycogen stores
  • limits exercise intensity
  • decreases time to exhaustion
  • increases rating of perceived exhaustion during physical activity (Nieman 1987)
• An average person stores enough glycogen to last for 12 to 14 hours or over 2 hours with sustained moderate intensity.
  • Mean ingested daily is 400 grams
  • To maintain an adequate supply, a minimum of 100 grams of carbohydrates should be ingested daily (Sources)

Synthesis After Exercise

• Approximately 50% more glycogen can be stored if carbohydrates are consumed immediately following strenuous exercise as opposed to waiting 2 hours after exercise
  • Suggested amount
    • 100 g of carbohydrates (400 Kcal) for the average 175 lb man (Friedman 1991).
    • 10 – 20% of total daily caloric intake of carbohydrates and quality proteins in approximately 4:1 ratio
• Muscle glycogen synthesis is greater within 2 hours proceeding exercise (Friedman 1991) and greatest 45 minute post workout (Ivy JL 1988, Leven hagen DK 2001)
  • Exercise increases the muscle's sensitivity to insulin, predominately, during the 4 to 6 hours after exercise
  • During this time, muscle glycogen synthesis has been shown to be greater with ingestion of simple as compared with complex carbohydrates
  • After which, muscle glycogen can be resynthesized near pre-exercise levels within 24 hours, equivalently with either carbohydrates form.
• After 24 hours, muscle glycogen can increase very gradually, succeeding normal levels over the next few days (Ivy 1991).
• Super glycogen saturation technique can increase amount of work by 19%
  • Old method involved glycogen depletion through an initial low carbohydrate diet followed by a high carbohydrate diet
  • Newer method suggests glycogen depletion can be obtained by repeated, prolonged intense exercise with similar results
  • Repeated muscle glycogen supercompensation is not possible, however, performance enhancement is maintained (McInerney 2004)
  • Carbo-loading should not be done more than 3x/year
  • Preadolescent and adolescent individuals should not carbo-load
    • instead, just taper training volume and intensity days before an important event