Contractile Character of Muscle and Fatigue

Question 1

What is an isometric contraction?

Answer 1

Contraction generating force without shortening

Question 2

What is an isotonic contraction?

Answer 2

Change in length of the muscle fiber to generate force

Question 3

What is a concentric contraction?

Answer 3

Shortening contraction

Question 4

What is an eccentric contraction?

Answer 4

Lengthening contraction

Question 5

What four factors determine the contractile characteristic of muscles?

Answer 5

Duration of active state
Force-velocity relation
Length-tension relation
Fatigability

Question 6

What is the latent period?

Answer 6

When stimulated muscle processes are underway

Question 7

Is isotonic or isometric latent period longer?

Answer 7

Isotonic

Question 8

Why is the isotonic latent period longer?

Answer 8

Because it has to reduce the slack of tendons and elastic fibers from muscle

Question 9

What is contraction time?

Answer 9

Time to peak tension

Question 10

What is relaxation time?

Answer 10

Time to required for decay of the active state; determined by rate calcium returns to SR

Question 11

What is described by the length-tension relationship?

Answer 11

Muscles at different lengths stimulated will give different tension values

Question 12

What is described by the force-velocity relationship?

Answer 12

A loaded muscle will have a slower contraction velocity than a completely free muscle

Question 13

What causes the force-velocity relationship?

Answer 13

Cross-bridges maintaining the length can not contract; at lesser loads some CBs are left over to shorten the muscle at a slower velocity

Question 14

What is the ratio of ATP cost for one AP in type I vs type II muscle fibers?

Answer 14

1:3

Question 15

Why are FT muscles more costly?

Answer 15

Because they have much faster cross-bridge cycling

Question 16

What does the Henneman size principle state?

Answer 16

That motor units are activated in a fixed order

Question 17

Which size motor neurons are activated first?

Answer 17

Smaller motor neurons (Type I)

Question 18

What is a strong predictor of energy cost during walking?

Answer 18

The vertical displacement of the pelvis

Question 19

Why is speed decreased in amputees and obese patients?

Answer 19

Because the energy expenditure is greater so they must slow down to conserve energy; still use more energy when moving slower

Question 20

What is muscle fatigue?

Answer 20

Inability to generate a required force

Question 21

What are the two types of muscle fatigue?

Answer 21

Central and peripheral fatigue

Question 22

What is central fatigue?

Answer 22

Fatigue that occurs within the CNS to NMJ

Question 23

What is peripheral fatigue?

Answer 23

Fatigue that occurs from the NMJ to contractile force generating apparatus

Question 24

What can contribute to muscle fatigue?

Answer 24

Hydrogen ion conc. from lactate ion

Question 25

At what concentration of lactate does muscle fatigue typically occur?

Answer 25

18 mM

Question 26

What is an example of central fatigue?

Answer 26

When a task can not be continued but the muscles can produce the required force when directly stimulated electrically

Question 27

What is a list of factors that are involved in muscle fatigue?

Answer 27

Potassium ion
Decreased ATP
Inorganic Pi
Lactate and H+ (mostly H+)
Muscle pH
Muscle Glycogen Depletion
Reactive oxygen species

Question 28

What is the fatigue quotient?

Answer 28

Formula that takes into account the influence of the 3 biomechanical systems that are the basis of muscle function

Question 29

How is the value of a fatigue quotient evaluated?

Answer 29

The lower the ratio the more fatigue resistant a muscle is