Factors of Muscle Contraction Study Guide

Question 1

Force of muscle contraction depends on……..

Answer 1

Number of formed cross bridges

Question 2

What are the 4 factors that affect the number of cross bridges?

Answer 2

1. Number of muscle fibers stimulated (recruitment) – the more motor units recruited, the greater the force of contraction
2. Relative size of fibers – the bulkier the muscle, the more tension it can develop
3. Frequency of stimulation – the higher the frequency, the greater the force of contraction
4. Degree of muscle stretch – muscle fibers at 80-120% of their resting length generate the most force

Question 3

Define the length-tension relationship. What does this mean at the level of the myofilaments?

Answer 3

• Muscle fibers with sarcomeres that are 80-120% of their normal resting length generate the most force
• Sarcomeres that are less than 80% of their resting length have too much filament overlap and force decreases
• Sarcomeres that are greater than 120% of their resting length have too little filament overlap and force decreases

Question 4

What are the two functional characteristics used to categorize muscle fibers by type?

Answer 4

• Speed of contraction (slow vs fast fibers)
  
  • How fast ATPases split ATP
  • Pattern of electrical activity of motor neurons
• Metabolic pathways used to atp synthesis
  
  • Oxidative fibers use aerobic pathways
  • Glycolytic fibers use anaerobic pathways

Question 5

What are the three muscle fiber types? Which of these types use aerobic pathways for ATP synthesis? Which use anaerobic pathways?

Answer 5

• Slow oxidative fibers: AEROBIC PATHWAYS
• Fast oxidative fibers: AEROBIC (some anaerobic glycolysis)
• Fast glycolytic fibers: ANAEROBIC GLYCOLYSIS

Question 6

How is the % that we have of each muscle fiber type determined? Can it be changed

Answer 6

• % we have of each muscle fiber type is determined by genetics
• % of each fiber type can be modified by performing certain types of exercise

Question 7

Is the % of each muscle fiber consistent throughout a muscle? Or a motor unit?

Answer 7

• most muscles contain a mixture of fiber types – results in a range of contractile speed and resistance to fatigue
• all the muscle fibers in 1 motor unit are the same type

Question 8

Think about what types of muscle fibers would be best at completing different activities.

Answer 8

Slow oxidative fibers: low intensity endurance activities
- Maintaining posture, running a marathon
Fast oxidative fibers: medium intensity activities
- Sprinting, walking
Fast glycolytic fibers: short, intense/powerful movements
- Hitting a baseball

Question 9

Higher recruitment will cause ________ contraction and _____– duration of contraction.

Answer 9

• faster
• longer

Question 9

A greater load will cause _____ contraction and _____ duration of contraction.

Answer 9

• slower
• shorter

Question 10

List and learn the physiological changes you can expect in response to regular resistance activity.

Answer 10

• Muscle hypertrophy – primarily due to increased size of individual muscle fibers
• Increased number of mitochondria, myofilaments, glycogen stores, and connective tissue
• Regular resistance activity can convert fast oxidative fibers to fast glycolytic fibers (2A→2B)
• Increased overall muscle strength and size

Question 11

List and learn the physiological changes you can expect in response to regular endurance activity.

Answer 11

• # of capillaries surrounding the muscle fibers increase
• # of mitochondria within the muscle fibers increases
• Muscle fibers synthesize more myoglobin
• These changes will be most dramatic in slow oxidative fibers
• Muscles have greater endurance, resistance to fatigue, and strength
• With repeated endurance exercise, some fast glycolytic fibers may convert to fast oxidative fibers (2B → 2A)

Question 12

What is disuse atrophy?

Answer 12

Degeneration and loss of muscle mass due to immobilization or loss of neural stimulation
- Muscle strength declines up tp 5% a day, causing muscles to atrophy