Question Answer
Methods for determination of muscle action Anatomical lines of pull
Anatomical dissection
Palpation using sense of touch to examine muscle when contracted
Superficial muscles ONLY
Understanding joing mechanics
EMG detects AP from muscles and provides readout of contraction intensity and duration
Most accurate way of detecting presence and extent of muscle activity
E-Stim Reverse of EMG
Use electricity to CAUSE muscle activity
Joint actions may then be observed to see the effect of the muscle's contraction
Contraction of muscle occurs at Muscle fiber level within a particular motor unit
Motor unit Single lower motor neuron
Muscle fibers it innervates
Functions as a single unit
Typical Muscle Contraction # of motor units responding & # of muscle fibers contracting w/in muscle may vary sig from few to all
depends on # of muscle fibers w/in each activated motor unit and # of motor units activated.
All of None Principle Individual Fibers within a given motor unit will either fire and contract maximally or not at all
Difference between lifting minimal vs. maximal resistance is in… the # of muscle fibers recruited.
# of muscle fibers recruited may be increased by activating motor units containing greater # of muscle fibers
Activating more motor units
increasing frequency of motor unit activation
# of muscle fibers per motor unit varies sig From >10, requiring preciseness such as eye to a few thousand in large muscle that perform less complex activities (QUADS)
Factors affecting muscle tension development Motor unit must first receive a stimulus via electrical signal know as an AP for the muscle fibers to contract.
Subthreshold Stimulus Not strong enough to cause AP
NO contraction
Threshold Stim Stimulus strong enough to produce an action potential in a single motor unit axon
All muscle fibers in that unit contract
Submaximal Stim Stim strong enough to produce AP in more than 1 motor unit
Maximal Stim Stim strong enough to produce AP in all motor units of a particular muscle
As Stimulus strength increases from threshold up… more motor units are activated
overall muscle contraction ^ in a graded fashion
Phases of a single muscle fiber contraction 1. Stimulus
2. Latent Period
3. Contraction Phase
4. Relaxation Phase
Latent period 3 ms
Contraction phase Muscle fiber begins shortening
40 ms
Relaxation phase 50 ms
Summation Successive stimuli are provided before relaxation phase of 1st contraction is completed.
Subsequent twitches combine with first to produce a sustained contraction
Produces greater amnt of T
As f of stim ^ summation ^ producing an increasingly greater
Tetanus Stimuli are provided at frequency high enough that no relaxation can occur between contractions
Treppe Multiple Max stimuli at low frequency allow complete relaxation between contractions.
Slightly greater T is produced by 2nd stim, etc
Staircase effect
Resultant Contractions after initial ones result in = T being produced.
Muscle Length-Tension relationship Max ability of muscle to develop T and exert force varies depending on length of muscle during contraction
Proportional decrease in ability to develop T occurs as muscle is shortened
Stretched 100%-130%, greatest T
Shortened 50%-60% T=0
Muscle Force-Velocity Relationship When muscle is contracting (conc. or ecc.) the rate of length of change is sig related to the amount of F potential
As velocity of action ^, total T produced by muscle decreases
When load is min, V of muscle contraction is max…….
Muscle Force Velocity cont'd As Load or Force increases, the velocity of the muscle contraction slows to zero, then the muscle begins to lengthen after that. As the force needed to control mvmnt ^, V of eccentric lengthening ^ until control is lost
Concentric Velocity and Force Production Relationship is Inverse Relationship
Eccentric Velocity and Force Production Relationship is Proportional Relationship
Angle of Pull Angle between the line of pull of the muscle and the bone on which it inserts (Angle toward joint)
With every degree of joint motion, the angle of pull changes
Joint movements & insertion angles involve mostly small angles of pull
Angle of Pull 2 Angle of pull decreases as bone moves away from it's anatomical position
ROM depends on type of joint and bony structure
Most muscles work at angles of pull less that 50 degrees
Amount of muscle F needed to cause joint mvmnt is affected by angle of pul
Rotary Component Vertical component
Component of muscular F that acts perpendicular to long axis of bone
When line of muscular F is at 90 degrees to bone on which it attaches, all of the muscular force is rotary force
All F is being used to rotate the lever about axi