Glycogen

ExRx.net > Diet > Outline

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


Main Menu | Carbohydrates | Nutrition Titles