Muscle terminology Flashcards
What is force and how do you calculate force?
Linear changes the motion state of a body of mass
Mass * acceleration
What is torque and how do you calculate it?
rotational or angular equivalent of force
Force * moment arm (dma)
Axis of rotation needed
What is axis of rotation
A point where things rotate upon/ around
Axis or rotation
Frontal, sagittal and longitudinal
What is the moment arm?
The moment arm is the perpendicular (90 degrees) distance between the line of action of the force to the axis of rotation.
For skeletal muscle it is the distance from the joint’s axis of rotation to the muscles force vector, drawn at a right angles to the vector.
What angle must the moment arm be to the line of action?
90 degrees.
Why do people change moment arms?
Damage to the spinal chord at cervical tissue resulting in a loss of function e.g. wrist
Loss of balance at the wrist, flexed and ulnar deviated.
After tendon transfer
Increase in wrist extension
moment arm has an increase in wrist extension strength
• Changed moment arm from ulnar to radial deviator
Increase in radial deviation .strength
Muscles develop tension and shorten or attempt to shorten. How do they lengthen?
They can lengthen themselves, external forces are required such as gravity or antagonist muscles of engages muscle.
3 types of contractions
Concentric
Eccentric
Isometric
Concentric contraction
Where muscles develop tension and shorten resistance to shortening are overcome. Occurring during lifting type actions.
Eccentric contraction
Eccentric contraction
Occur when muscles develop tension but lengthen. External forces overcome those created by muscles. This occurs when we lover objects.
Isometric
Muscles develop tension but remain at the same length. Limb or trunk segments are maintained stationary despite forces that tend to cause
muscle lengthening. Or muscles work against loads that can not be lifted. No mechanical work done (W = F x d)
Agonist muscle?
Muscle that contracts to cause desired/observed action.
Antagonist muscle?
Muscle that contracts to oppose the desired/observed action.
What is a prime mover
The most ‘effective’ muscles in a movement
Pec. major & Ant. Delt. in horizontal shoulder flexion
What is an assistant mover?
Less ‘effective’ muscles that ‘help out’.
Coracobrachialis & middle deltoid in horizontal shoulder flexion.
What dictates “effectiveness” of muscle at producing a particular movement?
Torque = Force x moment arm
What are the 2 key principles of 2 joint muscles
- When a muscle contracts and shortens it wants to produce all its desired actions
- Just because a particular joint action is present, dosent mean that all muscles that contribute to that joint action will be activated. This is because the nervous system knows that sometimes it is better to activate some agonists (movement can also occur by gravity and momentum).
What are the 2 exceptions for single joint muscles that have principles of 2 joint muscle?
- biceps brachii during simultaneous shoulder extension and elbow flexion.
- gastrocnemius during simultaneous ankle plantar-flexion and knee extension
Exception of the bicep brachii
Some movements require simultaneous shoulder extension and elbow flexion.
Biceps brachii presents an exception to the two-joint rule
Beneficial effect on elbow flexion substantially outweighs negative
effect on shoulder extension
Net effect of recruiting biceps brachii is greater strength in movement
An example of this is rowing, you are pulling the paddles towards your chest (elbow flexion) as well as pulling your shoulders back (shoulder flexion)
2 key principles of stabilization synergy
- When a muscle contracts and shortens, it “wants” to produce all of its
actions - What a muscle can do is not an indication of what it will do
What is stabilization
Muscles acting isometrically to ‘stiffen’ joints & prevent unwanted
movement.
An example is your trunk and vertebrae.
When you are standing upright the mass of your trunk and gravity causes trunk flexion the trunk extensor automatically isometrically oppose gravity.
What are some sources of unwanted movement with stabilizers
gravity and muscles
What are the 2 types of synergy
Helping and true
Helping synergy
Muscles with one or more common & one or more opposing action act together (to create the common action).
True synergy
One or more actions of a multi-action muscle is prevented by the action(s)
of another muscle which does not contribute to the observed movement.
True synergy in single joint muscle (shoulder pecs)
The pectoralis major performs horizontal shoulder flexion, needed in a bench press.
Also produces shoulder internal rotation which is not desired (unwanted movement).
We need a muscle that performs shoulder external rotation without
interfering with horizontal shoulder flexion.
Shoulder external rotators:
• Infraspinatus
• Teres minor
