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Chapter 12

BPK 143 Chapter Notes - Chapter 12: Intramuscular Fat, Carbohydrate Metabolism, Myocyte


Department
Biomedical Physio & Kines
Course Code
BPK 143
Professor
Tony Leyland
Chapter
12

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FACTORS GOVERNING THE SELECTION OF FUELS FOR MUSCULAR WORK
- Carbohydrates and fats are the major fuels used during exercise
- Percentage utilization of fats, carbohydrates, and proteins in energy metabolism during exercise
depends on the following factors:
1) Intensity of exercise
- At rest, about two-thirds of the ATP produced in muscle tissue is derived from the breakdown of fatty
acids, while the other third is derived from the breakdown of glycogen and glucose
- Protein is not used as an energy source unless you are severely deficient in carbohydrate and not
adapted to such a diet
- At 20% of , approximately 60% of the energy comes from fat
- at 50% of , only about 40% of the energy comes from fat
- At work levels above 95% , carbohydrate is used almost exclusively
Typical muscle glycogen utilization at various exercise intensities
2) Duration of exercise
- At exercise intensities between 65% and 85% of , it commonly takes 80120 minutes to deplete
muscle glycogen stores
- For athletes performing long-duration events, there is a real danger that they will deplete too much
glycogen before their event is completed
- As exercise duration increases, the proportion of energy production from fats begins to increase
- There will be a gradual increase in the bodys reliance on fat as a source of fuel
- At lower power outputs, a greater PERCENTAGE of fat is burned, not ABSOLUTE values of fat

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Carbohydrate (CHO) and fat metabolism during prolonged exercise
Glucose metabolism versus exercise duration
- The longer the event ( lower power output), the lower the percentage of energy will be obtained from
glycogen
3) State of physical training and fuel utilization
- The higher the subjects , the greater the contribution of fatty acids to energy production at any
given workload or running speed
- For any given workload, the fitter person will be at a lower percentage of his or her than the
less fit person
- Endurance training brings about enzymatic adaptations in trained muscle fibres
- Allows aerobically fitter individuals to get a greater proportion of energy production from fats at any
given percentage of compared with the same percentage of for the less fit person
- It is the glycogen-sparing effect in endurance training
- In long-distance race, athlete who is fitter will not deplete glycogen stores as quickly and thus will go for
a longer time at a faster pace

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DIETARY CARBOHYDRATE
- The amount of carbohydrate in the diet will affect the amount of glycogen stored in the muscle fibres
- Muscle glycogen levels at the start of moderate-to-high-intensity endurance exercise have a major
effect on the length of time for which the exercise can be continued
- Muscle glycogen content is positively related to work performance
Relationship of exercise to volitional exhaustion and muscle glycogen on three diets
- Carbo-loading: eating a large amounts of carbohydrate in the days prior to an endurance race
- Athletes engaging in intense daily training, which relies heavily on muscle glycogen reserves, ensure
that they obtain adequate carbohydrates in their diet
- While brief spikes in carbohydrate intake may be beneficial, chronically high carbohydrate intake may
be as detrimental for athletes as it is for the general public
- If going with high-carbohydrate diets, at least go with natural foods
- The type of carbohydrate ingested during the 24-hour period between exercise training sessions does
not differentially affect muscle glycogen synthesis
- Complex carbohydrates may be superior to simple carbohydrates during a three-day period of diet
manipulation to super-compensate or overload liver and muscle glycogen stores
- It is better to eat complex carbohydrates such as rice, potatoes, bread, and so on than to consume
simple sugars that are found in candies and soft drinks
CARBOHYDRATE LOADING (GLYCOGEN SUPER-COMPENSATION)
- High glycogen levels can delay when athletes must slow down because of muscle glycogen depletion,
thereby improving race times
- Shorter duration events typically do not benefit from these specific dietary regimes
- Depleting glycogen stores prior to the pre-event tapering (resting) period will result in higher pre-event
glycogen stores
- In effect, the body senses the low glycogen levels and is hungry to store carbohydrate when it gets
the chance
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