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DING DING DING - BELL RINGER!!! 1. Fats contain ______ calories per gram of energy. 2. Excess sugar consumption is unhealthy because it is converted to _______________. 3. The body contains no protein stores. All protein in the body is functional as ______________ or ______________.

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DING DING DING - BELL RINGER!!!

1. Fats contain ______ calories per gram of energy.

2. Excess sugar consumption is unhealthy because it is converted to _______________.

3. The body contains no protein stores. All protein in the body is functional as ______________ or ______________.

4. It can take from ________________ for the body to reach steady state VO2 levels.

5. Oxygen deficit is _______________ (greater/less) for untrained athletes.

6. Name two factors that contribute to EPOC.


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Energy Systems and Sports

Sports vary widely in both intensity and duration. Analyze the following activities, and access which is their predominant energy system.

  • cross country skiing

  • bowling

A

An

A

An L/A

An L

An

An L

An L

A

An

An

An

An/A

An

An

An

A

An

An

An L

An

An L/A

  • alpine skiing

  • badminton

  • cross country running

  • javelin throw

  • basketball

  • 50 m swimming

  • volleyball

  • discus

  • curling

  • 2 km swimming

  • dancing

  • 100 m sprint

  • 800 m running

  • wrestling

  • 5 km rollerblading

  • 200 m sprint

  • football

  • golf

  • high jump

  • soccer


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Exercise and Blood Lactate Levels

As the intensity of exercise increases, the body cannot maintain aerobic ATP production. At about the same time it has been observed that blood lactic acid levels starts to rise exponentially. This phenomenon has been named the lactate threshold.

In untrained athletes, this point is reached more quickly (50% – 60% of VO2 max).

In trained athletes it occurs at higher work rates (65% – 85% of VO2 max).


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Lactate vs Anaerobic Threshold

The use of the term anaerobic threshold to denote the increase in blood lactate levels implies that it coincides with increased reliance on the anaerobic energy system.

This over-simplifies the situation as increased lactate levels could result from:

  • Accelerated glycolysis resulting in a backup at the mitochondrial membrane.

2. Fast Twitch fibres contain more active enzyme that favours the conversion of pyruvate to lactate.

3. Slow rate of removal of lactate from the blood.

4. Low muscle oxygen.

For these reasons, the use of the term lactate threshold has become the more accepted term to describe the exponential increase in blood lactate levels during increasingly intense exercise.


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Muscle Fatigue

Muscle fatigue -

reduction in force production during short-term high intensity or prolonged low intensity exercise

Historically, lactate (lactic acid) has had a bad reputation, being blamed for painful muscle soreness and the impairment of muscle contraction. These effects were blamed on the decrease in pH brought on by the strong acidic nature of lactic acid. This seemed to make sense since increased lactate production, increased exercise intensity and increased fatigue go hand-in-hand.

However, research has shown that muscle fatigue has many causes and depends on the intensity of activity.

As for lactate and muscle soreness, it seems to be correlation not causation. Lactate is actually an important source of glucose synthesis (gluconeogenesis) in the liver.


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Muscle Fatigue

Factors contributing to muscle fatigue:

During high intensity exercise

  • Accumulation of hydrogen ions impairs Ca2+ binding with troponin. This meansfewer strong binding sites are exposed.

2. Increased amount of inorganic phosphate (Pi) impairs crossbridge cycling.

During prolonged low intensity exercise

Failure of excitation contraction coupling due to a reduction in

the release of calcium from the sarcoplasmic reticulum.


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Prolonged Exercise and Blood Lactate

The lactate threshold can be shifted (increased) with intense exercise training. That is, the amount of work at which lactate starts to increase exponentially in the blood is increased.


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The Cori Cycle and Lactic Acid

The Cori cycle is the process where lactic acid createdin themuscle during anaerobic activity is transported to the liver where it is converted back to pyruvate and then to glucose (gluconeogenesis). It is then released back into the blood to be used in the future as an energy source.

Note: Because the process requires energy (ATP) to proceed, it takes place in the 30 – 40 mins following activity when the O2demand for ATP resynthesis can be met.


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DING DING DING - BELL RINGER!!!

1. Is lactate responsible for muscle soreness and failure?

NO

2. At what percentage of VO2 do untrained athletes reach lactate threshold?

50 – 65% VO2 max

3. Name two factors that could be responsible for elevated blood lactate levels.

Type II fibres - more active enzyme pyr → Lactate

Accelerated glycolysis

Low muscle oxygen

Slow Lac. removal

4. What two factors contribute to muscle fatigue during high intensity activities?

Hydrogen ion buildup

Inorganic phosphate buildup

5. Name the process that takes place in the liver involving the generation of glucose from lactate.

Gluconeogenesis


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Fuel Selection During Exercise

There are many factors that determine what the body uses for fuel. Three of the main factors are:

1. Diet

2. Exercise Intensity

3. Exercise Duration

1. Diet

  • high fat, low carbohydrate diets → Fats


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2. Exercise Intensity - Crossover Point

  • Low intensity exercise (<30% VO2 max) → Fats

  • Highintensity exercise (<70% VO2 max) → Carbohydrates

Crossover point -

the exercise intensity at which the energy derived from carbohydrates equals that of fat

Crossover point

Carbs

As the exercise intensity increases above the crossover point, there is a shift from fat to carbohydrate metabolism.

Fats


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Exercise Intensity & Fuel Selection

What causes the shift from fat to carbohydrate metabolism as intensity increases?

1. Recruitment of Fast twitch muscle fibres.

  • high glycolytic enzyme activity

  • few mitochondria and lipolytic enzymes

Crossover point

2. Increasing levels of epinephrine in the blood.

  • increases rate of glycolysis


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3. Fuel Selection & Exercise Duration

During prolonged low-intensity exercise (>30 mins) there is a shift from carbohydrate to fat metabolism.

Lipolysis – breakdown of fats into Free Fatty Acids

(FFA) and glycerol by enzymes called lipases

Crossover point

Increased rate of epinephrine in the blood, increases lipase activity.

This process is inhibited by insulin and lactate. Therefore, after a high carb meal or drink, lipolytic activity is diminished as insulin is released to reduce blood sugar levels.


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Interaction of Fat and Carbohydrate Metabolism

Prolonged exercise (>2 hours) results in a decrease in depletion of muscle and liver glycogen stores.Depletion of these stores results in muscle fatigue.

WHY?

Aerobic production of ATP requires pyruvate which is produced via glycolysis from the breakdown of muscle and liver glycogen (carbohydrate).

Low levels of pyruvate mean that the Krebs cycle cannot function at full capacity and therefore the production of ATP is reduced.

This results in a reduced rate of fat metabolism as fat metabolism happens via the Krebs cycle, hence . . .

“Fats burn in the flame of carbohydrates”.


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MUSCLE FATIGUE!!!

 No FAT METABOLISM

Interaction of Fat and Carbohydrate Metabolism


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ANS:

Yes! The reasons are twofold. Firstly, by ingesting carbohydrates (glucose), glycolysis can continue. While little ATP is generated directly by glycolysis, the generation of pyruvate enables the Krebs cycle to resume resulting in aerobic ATP production from carbohydrates. Secondly, with the Krebs cycle operational, fat metabolism can continue resulting in additional aerobic ATP generation!

Sports Drinks and Performance

Consider what you know about carbohydrate and fat metabolism as well as the relationship between them. . .

Do you think a carbohydrate based sports drink would have any benefit during prolonged, sub-maximal activity? Explain.


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Body Fuel Source Breakdown

Carbohydrate Sources:

  • glycogen (muscle, liver)

  • blood glucose

Fat Sources:

  • Fatty acids (Blood Plasma)

  • Muscle triglycerides

Protein Sources:

  • skeletal muscle (small amount)

*Lactate:

  • skeletal, cardiac muscle



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