Factors of Muscle Contraction

Question 1

force of muscle contraction

Answer 1

depends on the # of formed cross bridges
- # of cross bridges is affected by 4 factors
1. # o f 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 more force

Question 2

length-tension relationship

Answer 2

• muscle fibers w 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 3

velocity and duration of concentration

Answer 3

muscles vary in how fast they can contract and for how long they can continue to contract
these characteristics are influenced by:
- muscle fiber type
- load
- recruitment

Question 4

muscle fiber type

Answer 4

classified according to 2 functional characteristics
1. speed of contraction (slow vs. fast fibers)
- how fast atpases split atp
- pattern of electrical activity of motor neruons
2. metabolic pathways used for atp synthesis
- oxidative fibers use aerobic pathways
- glycolytic fibers use anaerobic glycolysis

Question 5

muscle fiber type

Answer 5

classified into 3 types
- slow oxidative fibers
- fast oxidative fibers
- fast glycolytic fibers
*most muscles have a mixture of fiber types determined by genetics but can change the percentage of each w certain exercises
- different atp synthesis pathways used by each fiber type

Question 6

slow oxidative fibers

Answer 6

low intensity, endurance activities
- ex. maintaining posture, running a marathon

Question 7

fast oxidative fibers

Answer 7

medium-intensity activites
- ex. sprinting, walking

Question 8

fast glycolytic fibers

Answer 8

short, intense or powerful movements
- ex. hitting a baseball

Question 9

load and recruitment

Answer 9

with higher recruitment - more motor units contracting - a faster and prolonged contraction will be produced

Question 10

aerobic (endurance) exercises

Answer 10

ex. swimming, running, fast walking, cycling
- # of capillaries surrounding the muscle fibers increases
- # of mitochondria within the muscle fibers increases
- muscle fibers synthesize more myoglobin
- these changes will be most dramatic in slow oxidative fibers
- with repeated endurance exercise, some fast glycolytic fibers may convert to fast oxidative fibers

Question 11

resistance exercise

Answer 11

ex. weight lifting, isometric exercises
- muscle hypertrophy - primarily due to increased size of muscle fibers
- increased # of mitochondria, myofilaments, glycogen stores, and connective tissue
- regular resistance activity can convert fast oxidative fibers to fast glycolytic fibers

Question 12

disuse atrophy

Answer 12

degeneration and loss of muscle mass due to immobilization or loss of neural stimulation
- can begin almost immediately
- muscle strength can decline ~5% per day
- paralyzed muscles - without any neural stimulation - can atrophy to 1/4 initial size