Physiology: Muscular Work Flashcards
(41 cards)
What does the amount of movement that a muscle can produce depend on?
the original length of its fibers
What happens to muscle fibers during movement?
Muscle fibers reduce in length.
What is the most familiar characteristic of muscle work?
muscle strength
What force does a muscle produce when it shortens?
a tensile force
What does muscle force produce?
the tendancy to rotate
What two factors are used to describe a muscle strength?
1) the ability to generate a tensile force (the force a muscle creates when it shortens)
2) the ability to create a rotation
How is the assessment of muscle strength in vivo typically performed?
by the determination of the amount of weight a subject can lift.
What device is used to determine the amount of weight a subject can lift?
isokinetic dynamometer
What does the force of muscle contractions depend on?
- length-tension relationship
- size of the muscle
- number of motor units
- the frequency of stimulation
- the angle of the joint
When is the maximal force generated in the LENGTH-TENSION RELATIONSHIP?
When the muscle is stretched to a length approximately 20% grater than its resting length.
When is the maximal force generated in the SIZE OF MUSCLE?
Large muscles have more muscle fibers, and therefore generate more force tha smaller muscles.
When is the maximal force generated in the NUMBER OF MOTOR UNITS RECRUITED?
The smooth and stready increase in muscular tension is produced by increasing the number of active motor units.
When is the maximal force generated in the FREQUENCY OF STIMULATION?
- single twitch
- summation of twitches (second contraction is larger than the first)
When is the maximal force generated in the ANGLE OF THE JOINT?
each joint has an optimum angle of force application.
What does the joint’s optimum angle of force application depend on?
The relative positions of:
- the tendinous insertions on the bone,
- the load being moved.
What does the tension produced by a sarcomere depend on?
the number of actin-myosin cross-bridges it forms.
How do muscles create force?
by cycling myosin cross-bridges
State the equation of cross bridge formation.
A + M + ATP –> A + M + ADP + Pi + force
A- actin
M- myosin
What does the number of cross-sections depend on?
the length of the sarcomere.
(It determines the amount of overlap there is between myosin and actin)
What is the most important factor determining the tensile force generated by a muscle’s contraction?
muscle size
Is the overall size of a muscle a good indicator for the number of fibers contained in the muscle?
No, it is a poor indicator.
Explain the relationship between muscle size and force of contraction.
complicated
What do the properties of the whole muscle depend on?
- the properties of fibers
- organization of the fibers
How are muscle fibers arranged in relation to the muscle’s line of action?
oblique to the muscle’s line of action (rarely run the whole length).
