Fuels and Fatigue

Question 1

Compare and contrast the properties of different muscle fibre types

Answer 1

The different types of muscle fibres are sequentially activated in the progression of light activity to maximal activity:

Type 1 -> Type 2a -> Type 2b

There is a greater percentage of type 2 fibres in sprinters; whereas marathon runners and cross country skiers tend to have greater proportions of Type 1 fibres

Myosin ATPase can be histochemically stained for in muscle to determine the fibre types present within a muscle section: Type 1 fibres stain dark after acidic pre-incubation; whereas Type 2 stain dark after alkaline pre-incubation

Question 2

What physiological changes are responsible for the observed skeletal muscle hypertrophy following resistance training?

Answer 2

The early and rapid improvements in strength following resistance/strength training is the result of improved neuromuscular coupling of pre-existing muscle mass.

Increased muscular mass does not occur until later in training

Question 3

What is the correlation between muscle mass and dissuse?

Answer 3

Individuals will lose muscle mass through inactivity

See the attached image for the pathway involved in regulating muscle mass

Foxo regulates atrophy of muscle; mTOR regulates muscle hypertrophy

The mechanisms that determine muscular mass are of great interest as therapies for wasting conditions and immobile patients:

• Development of passive movement machines and electrical stimulation of muscle currently as therapeutics

Question 4

List the mitochondrial adaptations that occur in response to exercise/aerobic training

Answer 4

Increased mitochondrial density and oxidative enzymes

Reduced CHO use and lactate production

Increased fat oxidation

Enhanced endurance performance

Improved sensitivity/action to insulin

Note: These adaptations are thought to occur as a result of stimuli, signalling and transcriptional regulation upon sustained endurance training

Question 5

What determines the power of a metabolic fuel?

Answer 5

The power of a metabolic fuel is determined by the rate at which it is capable of producing ATP

From most powerful to least powerful:

PCr = Glycolysis > CHO oxidation > FFA Oxidation

Question 6

What determines the capacity of a metabolic fuel?

Answer 6

The capacity of a metabolic fuel is the total amount of ATP capable of being produced by a stored fuel

From highest capacity to lowest capacity:

FFA Oxidation >>> CHO oxidation > Glycolysis > PCr

Question 7

Discuss the fuel sources relied upon for endurance exercise

Answer 7

Endurance exercise is capable of utilising oxidative fuel supplies including CHO, fats and proteins

Mainly relies on CHO and fat fuels

There is a much heavier relience upon muscle glycogen stores as activity intensity elevates

A reduced relience on fat occurs as the intensity of activity increases.

Question 8

Explain the concept of glycogen sparing

Answer 8

Glycogen sparing is the concept of upregulating the body’s use of fat fuels during exercise in order to retain as much CHO stores as possible, for as long as possible.

Ultra marathon runners attempt to run at 50-60% of vMax to exercise at a 50/50 CHO/fat utilisation

Question 9

What factors influence exercise metabolism?

Answer 9

Exercise intensity and duration

Diet

Training

Environmental Temperature

Age and Gender

These effects are mediated by substrate availability. hormone levels and biochemical characteristics of skeletal muscle

Question 10

What is fatigue?

Answer 10

Fatigue is a reversible and self-limiting state characterised by an inability to maintain the required or expected force and power output of muscle contraction in activity

To overcome fatigue, one must:

1. Change the required force (do less intense activity)
2. Reduce the time of activity (shorter duration of activity)
3. Increase the maximal force or power (requires training of muscles)

Exercise testing is used to stress a person to identify underlying physiological problems before symptoms at rest develop

**Muscle weakness **is the chronic reduction of muscle strength at rest due to an underlying pathological problem

Question 11

In what ways can the onset of fatigue be delayed?

Answer 11

The onset of fatigue can be delayed, but not prevented, by a number of different means:

Muscle glycogen is the predominant limiting factor of fatigue -> carbohydrate ingestion (+ CHO loading) can improve exercise capacity

**Training, nutrition, heat acclimistisation and drugs/supplements and gene doping **