Human Phys 2.8

Question 1

Force summation

Answer 1

Increase in contraction intensity as a result of the additive effect of individual twitch contractions

Question 2

What are the two ways to increase force summation?

Answer 2

Increase in number of motor units

Increase in the frequency of contraction (action potential firing)

Question 3

Staircase effect

Answer 3

Increase in the tension and force generated in the muscle with each subsequent action potential

Question 4

What happens if action potential frequency is sufficiently high?

Answer 4

Individual contractions are not resolved and a fused tetanus contraction is recorded

Question 5

Hypertrophy (common, weeks)

Answer 5

Caused by weight lifting

Increase in actin and myosin

Myofibrils split (thickness will increase)

Question 6

Hyperplasia (rare)

Answer 6

Formation of new muscle fibers (endurance training)

Question 7

What increases with hypertrophy and hyperplasia?

Answer 7

Force generation

Question 8

What is there no change in for hypertrophy and hyperplasia?

Answer 8

Shortening capacity or maximum velocity of contraction

Question 9

Lengthening (normal)

Answer 9

Occurs with normal growth

No change in force development

Increased shortening capacity

Increased maximum contraction velocity

Question 10

What are the causes of atrophy with fiber loss?

Answer 10

Denervation/neuropathy

Tenotomy

Sedentary

Cast

Space flight

Question 11

What are consequences to muscle performance with atrophy?

Answer 11

Degeneration of contractile proteins

Decreased max force of contraction

Decreased velocity of contraction

Question 12

Atrophy with fiber loss

Answer 12

Disuse for 1-2 years (very difficult to replace lost fibers)

Question 13

What are the two mechanisms for achieving for summation?

Answer 13

Multiple fiber summation

Frequency summation