Skeletal Muscle Mechanics

Question 1

What are the determinants of muscle force production?

Answer 1

recruitment of motor units, 
muscle fiber type, 
muscle length, 
speed of contraction, muscle action, 
torque potential, 
muscle architecture, 
firing frequency,
fatigueability

Question 2

Describe the recruitment of motor units.

Answer 2

size principle - recruit small ones first then move up to larger as needed

Question 3

Classify each type of muscle fiber by the functional classification (oxidative capacity).

Answer 3

Type I - slow oxidative,
Type IIA - fast oxidative glycolytic,
Type IIx - fast glycolitic

Question 4

Classify each type of muscle fiber by the diameter size.

Answer 4

Type I - small,
Type IIa - intermediate,
Type IIx - large

Question 5

Classify each type of muscle fiber by the color.

Answer 5

Type I and IIa - red,

Type IIx - white

Question 6

Classify each type of muscle fiber by the capillary density.

Answer 6

Type I and IIa - dense,

Type IIx - sparse

Question 7

Classify each type of muscle fiber by the myoglobin content.

Answer 7

Type I - high,
Type IIa - intermediate,
Type IIx - low

Question 8

Classify each type of muscle fiber by the speed of contraction.

Answer 8

Type I - slow,

Type IIa and IIx - fast

Question 9

Classify each type of muscle fiber by the rate of fatigue.

Answer 9

Type I - slow,
Type IIa - intermediate,
Type IIx - fast

Question 10

What is the most important characteristic of muscle?

Answer 10

the ability to develop tension and to exert a force on the bony lever

Question 11

What is passive tension?

Answer 11

developed in the parallel component of the muscle, created by lengthening the muscle beyond slack length of the tissues

Question 12

What is active tension?

Answer 12

tension developed by the contractile elements of the muscle

Question 13

At which sarcomere length is isometric tension maximal?

Answer 13

at optimal length

Question 14

At which sarcomere length is isometric tension decreased?

Answer 14

lengthening beyond optimal length AND shortening beyond optimal length

Question 15

What describes the relationship between the velocity of a muscle contraction and force produced?

Answer 15

force-velocity relationship

Question 16

The force-velocity relationship provides an explanation for what type(s) of contractions?

Answer 16

concentric and eccentric

Question 17

During which contraction is the muscle shortening?

Answer 17

concentric

Question 18

During which contraction is the muscle lengthening?

Answer 18

eccentric

Question 19

What is it called when the whole muscle is activated and the bones to which it attached do not move?

Answer 19

Isometric contraction

Question 20

What happens to the bones in a concentric contraction?

Answer 20

move closer together

Question 21

What happens to the bones in an eccentric contraction?

Answer 21

move away from each other

Question 22

True/False: The amount of tension that can be developed in a muscle depends on the type of contraction.

Answer 22

True

Question 23

What are the factors affecting torque potential?

Answer 23

length of moment arm of muscle force,
length of the muscle,
Velocity of shortening or lengthening during dynamic movements

Question 24

Which of the following is true?

a. muscles produce force by active over a moment arm at the joint to produce torque
b. moment arm of the muscle can’t change with joint position
c. As the joint moves, the muscle length remains constant.

Answer 24

A is true.
B = can change which affects the torque produced
C = muscle length changes

Question 25

What is the reduced capacity in production of active tension across a joint occurring when muscles are placed on slack across another joint?

Answer 25

active insufficiency

Question 26

Describe an example of active insufficiency.

Answer 26

can’t keep a tight fist when moving from neutral position to flexion

Question 27

What occurs when an inactive, potentially antagonistic muscle is of insufficient length to permit full ROM at the joints crossed by the passive muscle?

Answer 27

passive insuffieciency

Question 28

Describe an example of passive insufficiency.

Answer 28

fingers curl when moving from wrist Ext to Flex

Question 29

What is the electrical activity of a muscle force (measured my an EMG) proportional to?

Answer 29

recruitment (which is proportional to muscle force)

Question 30

What are the advantages and disadvantages of isokinetic exercise and testing?

Answer 30

advantages: maximal loading thru ROM, safe, objective, reproducible measurement
Disadvantages: isolation, non-WBing, limited acceleration, mono-planar, cost, not functional, differences in exertion by performer

Question 31

Describe an example of the utilization of active insufficiency to isolate a muscle group.

Answer 31

both Gmax and hamstrings perform hip extension when knee is maintained in extension, but when knee is flexed, it puts the hamstrings in active insufficiency, giving preference to utilizing Gmax

Question 32

Passive insufficiency leading to tenodesis can allow what?

Answer 32

individuals (such as C6 quadriplegic) to regain a degree of functional opening of their hand while reaching (move wrist into flexion = fingers straighten/release) and closing of their hand for grasping (moving wrist into extension = fingers curl/grasp)