Physiology: Muscular Work Flashcards
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).
What is the peak force production? What is it related to?
- related to the physiological cross sectional area (PCSA)
What is the PCSA? What does it estimate?
PCSA- physiological cross sectional area
- estimates the sum of the cross sectional area of all the fibers
- standard measure
What is the PCSA approximately equal to?
The anatomical cross sectional area in parallel fiber muscle.
How does the PCSA compare to the anatomical crossection in pennate muscle?
PCSA»_space; anatomical cross sectional area
Compare the contraction force of pennate muscle and muscle with parallel fibers.
- PCSA is much larger in pennate muscle
- anatomical crossections are very similar
- all other factors are equal
- pennate muscle is capable of generating more contraction force
When exposed to stimuli from the nervous system, how is the response of muscles categorised?
- “all or none” law
- if enough individual fibers contract at one time then the entire muscle will contract.
What happens as workload on a muscle increases?
the muscle will reach a point at which it will be no longer able to contract (no matter how much electrical stimulation it recieves).
This point is called the “point of muscle overload”.
What is the point of muscle overload?
The point at which the muscle workload is so large that the muscle cannot contract any longer, no matter how much stimulation is given.
How can muscular work be considered?
- strength (power)
- endurance
What is strength?
The maximum amount of tension produced by a particular muscle or muscle group.
What is endurance?
The amount of time for which an individual can perform a particular activity.
What factors determine the muscular work capabilities of any skeletal muscle?
1) types of muscle fibers
2) physical conditioning/training
How is muscular work classified? State both names.
1) STATIC- isometric ‘same length’
2) DYNAMIC- isotonic ‘same tension’
Explain static work. State its other name. How is static work achieved? What does it lead to?
- a muscle remains contracted for a period of time, but there is no movement.
- isometric
- heavily contracted muscles squeeze blood vesseks restricting blood flow.
- no oxygen delivery, no removal of lactic acid (waste product)
- RESULT: muscular aches and pain
Explain dynamic work. State its other name. How is static work achieved? What does it lead to?
- rythmical contraction and relaxation of a muscle, reulting in movement.
- isotonic
- contractions and relaxations act as pumps for blood flow
- muscle is supplied with more blood, oxygen,
- lactic acid is removed from muscle at a greater pace
How is the work output calculated? Equation.
WP (gmm) = WL (g) x LH (mm)
WP- work performed by the isolated muscle
WL- weight which the muscle can lift
LH- weight lifing height
How is the work output calculated? In words.
The work output is estimated by multiplying the weight that the muscle can lift by the height of lifing.
