Option D unit D4 - Glycogen
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what is glycogen
Glycogen is converted to glucose in muscles for ATP generation during exercise
Glycogen content of specific skeletal muscle fiber types:
• Slow twitch (type I) - low glycogen content • Fast twitch type IIa - medium glycogen content • Fast twitch type IIb - high glycogen content • Low intensity exercise predominantly uses slow twitch muscle fibers = less oxygen (aerobic) • High intensity exercise predominantly uses fast twitch/type II muscle fibers = more glycogen (anaerobic)
carb digestion
• Glycogen is stored glucose (carbs). Different foods have different rates of carb digestion. • Glucose is released at different speeds from food we eat. • Glycemic Index (GI) : the ranking system for carbohydrates based on how quickly the glucose (sugar) enters the bloodstream after digestion –> High glycemic index = will enter the bloodstream faster and all at once –> Low glycemic index = enters the bloodstream slow and over time Does not depend on how much glucose Ex. 10 grams of glucose High = all 10 grams enter the bloodstream fast and at once Low = 2 grams enters the bloodstream slowly → takes longer for all 10 grams to enter the blow stream.
The relevance of GI with regard to carbohydrate consumption by athletes pre- and post competition:
• consuming foods containing carbohydrates before and after exercise may be beneficial in aerobic performance and recovery • Key is when do you want the glucose to impact the body • During exercise (ex. Running a race) = ASAP = high glycemic index foods • Before exercise = in a while = low glycemic index foods • Post workout = quick for faster recovery = high glycemic index foods to replenish glycogen stores faster
The interaction of carbohydrate loading and training programme modification prior to competition
Carb loading: used to maximize stored glycogen in muscles, requires training + nutrition More common in people that have significant time during competitions - ex. Marathon, cycling Training: * Complete and exhaustive session approximately ~ 1 week prior to the event * The training load is tapered over the remaining days Diet: * Approximately 7 to 4 days prior the diet is low in CHO (high in fat and protein) * This increases the activity of the enzyme glycogen synthase * Results in greater glycogen storage when CHO diet increases → because the body was starved from carbohydrates * The final ~ 2 days has a high CHO diet