Muscle Mechanics

Question 1

Do isometric contractions do work or have power?

Answer 1

They do no work and have no power

Question 2

How is an isometric contraction described?

Answer 2

This is when a muscle develops tension but stays the same length (because the ends are attached to immovable objects)

Question 3

Why does an isometric contraction do no work?

Answer 3

Because W= F(l). Since the muscle is attached to immovable objects at either end, it cannot change its length….therefore W=0

Question 4

What are isometric contractions involved in?

Answer 4

Maintaining posture

Question 5

In an isometric twitch, what offsets contractile element contraction so that there is no movement?

Answer 5

Stretching of Series Elastic elements (SE)

Question 6

When the contractile element of a muscle shortens, what does the series elastic element do to offset that?

Answer 6

It lengthens an equal distance…which leads to an isometric contraction

Question 7

Body movements require what type of contractions?

Answer 7

Both isometric and isotonic contractions

Question 8

What type of movement is isotonic contraction associated with?

Answer 8

It is associated with Body movement

Question 9

Describe isotonic contraction

Answer 9

The length of the muscle changes but the tension in the muscle is sustained.

The force of the contraction is at least equal to the load so that the muscle shortens

Question 10

Hoe is an isotonic twitch measured?

Answer 10

An isotonic twitch is measured by attaching the muscle to a moveable load

Question 11

For isotonic contractions, why do tension curves look different?

Answer 11

It depends on the load placed on the muscle….the greater the load, the higher the plateau and the greater the time lag between stimuli and the start of the muscle shortening

Question 12

What happens if the load exceeds the amount of force the muscle can generate?

Answer 12

An isometric twitch

Question 13

What is the sequence of events in an isotonic twitch?

Answer 13

1- Actin and myosin are activated and the cycling of cross bridges begins
2- the contractile element shortens
3- series elastic element lengthens
4- Tension builds up to equal or exceed the load
5- Load begins to move
6- Tension becomes constant
7- Contractile element shortens even more
8- Load moves (under constant tension)

Question 14

Do isotonic contractions do work?

Answer 14

Yes, because W= T(d)

Question 15

What are the four phases of an isotonic twitch upon stimulation?

Answer 15

1- Isometric tension development
2- Isotonic shortening
3- Isotonic relaxation
4- Isometic relaxation

Question 16

As the weight of an load of an isotonic twitch increases, what changes are made to the twitch?

Answer 16

1- the initial velocity of shortening decreases (the latent period also increases)
2- the amount of shortening decreases
3- the duration of shortening decreases

Question 17

What is Po?

Answer 17

This is the maximal isometric tension that can be generated at a given initial length and a given state of contractility

the larger the muscle the larger the Po because the larger number of cross bridges

Question 18

How can Po increase in skeletal muscle?

Answer 18

1- Increase with frequency of modulation
2- Recruitment of additional motor units
3- Initial lengths close to the optimal initial length

Question 19

Hoe can Po increase in cardiac muscle?

Answer 19

1- increased initial length

2- increased contractility

Question 20

When do myofibrils produce maximum work and power?

Answer 20

intermediate loads

Question 21

Can certain types of muscle fibers shorten faster than others?

Answer 21

Yes

Question 22

What is the “preload”?

Answer 22

The load required to stretch a muscle from its resting length (to it operating length)

Question 23

What is the total load?

Answer 23

The Preload + the Afterload

Question 24

What is the “afterload” equivalent to?

Answer 24

the afterload is equivalent to the total tension

Question 25

How are length-tension curves produced for isometric contraction?

Answer 25

They are produced by measuring the maximum tension that can be developed during an isometric twitch at varied lengths

Question 26

How are length-tension curves produced for isotonic contraction?

Answer 26

They are produced by measuring the maximum tension that can be developed during isometric twitches at varied initial lengths