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SKELETAL muscle is defined as muscle which is striated or striped,
indicating and ordered cell structure, of myosin and actin filaments,
and is generally under voluntary control, which has an action on the
skeleton or bones in the body.
In its relaxed form the muscle is at its maximum length and this is generally howthe tissue is found.
Stimulation generally causes contraction and a shortening and thickening of the
tissue.
As it is attached to a minimum of 2 points, the Origin (O) and the insertion (I) -
contraction brings these 2 points closer together. To reverse this, another
muscle must be attached to 2 different points which when they move together
cause a reversal of the position of the 2 or more affected bones.
So for each muscle there is an antagonist (opposing muscle) and inmany situations a synergist (a muscle which enhances the original
movement).
Examination of Skeletal Muscles - major groups
Questions for individual joint examination
1 functional limitation
2 SS -limited to one or more joints
3 onset - acute - related to a specific incident
- chronic - slow progressive increase of pain or reduced ROM
4 description of the causative agent if known e.g. accident
5 any prior MSS history of that joint or others
6 Systemic problems
For participation in sport/training activities MSS : for this examination unless
otherwise indicated the patient standing - facing the clinician in the anatomical
position.
CERVICAL SPINE / NECK - ROM tests the following groups of muscles
Scalenes/Colles/Trapezius upper fibres/Cervicis regions of ES and deep muscles
of the VC/Sternocleidomastoid
patient looks at the roof R extension
patient looks at the floor R flexion
patient looks over each shoulder R horizontal rotation
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head bends towards the shoulder - sideways R (shoulders kept still) lateral
flexion
SHOULDER (SCAPULA) - ROM tests the following groups of muscles
Levator Scapulae/Rhomboids/Serratus Anterior/Spinati muscles/Trapezius/Deltoid
observe symmetry of shoulder particularly the Acromioclavicular jt shrug
shoulders R elevation
drop shoulders depression
straighten shoulders - trying to meet shoulder blades lateral rotation
contract shoulders - withdrawing chest medial rotation
abduct shoulders to 90o (flexed arm) R abduction
SHOULDER + ARM - ROM tests the following groups of muscles
Pectorals/Latisimus Dorsi/Trapezius/Scapular muscles
scratch back with each hand from over and under the shoulder or have hands
meet at the back from over and under the shoulder external rotation +
abduction / internal rotation + adduction
move extended abducted arms as high as possible R vertical adduction
move extended abducted arms into the sagittal plane R horizontal
adduction
move extended abducted arms out of the sagittal plane R horizontal
abduction
with bent arms keep them close to the body against R adduction
UPPER LIMB + HAND - ROM tests the following groups of muscles
Brachii muscles/Brachioradialis/Flexors & Extensors of upper limb, hand &
digits/Supinators/Pronators/Carpi muscles/Intrinsic muscles of the hand
flex/extend elbows R, turn wrist in and out R pronation/supination
bend and straighten wrist R flexion/extension
move extended wrist towards the body R ulnar deviation = medial flexion
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move extended wrist away from the body R radial deviation = lateral
flexion
spread extended fingers R abduction
close extended open fingers Radduction
oppose fingers and thumb opposition
make a fist R flexion
extend hand and fingers R extension
BACK ABDOMEN - ROM tests the following groups of mscles
ES, deep muscles of the back, Latissimus Dorsi, Quadratus Lumborum, Obliques,
Gluteal muscles, Rectus Abdominus
observe posture, shoulder and neck symmetry, spinal curvature observe for
balance on one leg bend from side to side while facing the front lateral flexion
bend back as far as possible hyperextension
twist from the hips to the left & right rotation
supine patient - touch toes and back extension/flexion (back/abdomen)
HIP + THIGH - ROM tests the following muscles
Gluteal muscles/Iliopsoas /Obturators/Quadriceps/Hamstrings/
Adductors/Abductors
observe symmetry of the hips and stance turn leg inwards/outwards
medial/lateral rotation
standing patient - touch toes with straight legs extension/flexion (back) &
hamstring tightness
lift the extended leg forwards/backwards flexion/extension (hip)
lift the extended leg sideways lateral flexion (hip)
with the sitting patient keep legs together against R adduction
LOWER LIMB + KNEE + FOOT - ROM tests the following groups of
muscles
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Gluteal muscles/Iliopsoas/Quadriceps/Hamstrings/Adductors/Abductors/Peroneal
muscles/Soleus/Intrinsic muscles of the foot
observe for knee & ankle symmetry - looking for effusions &/or deformities bend
and straighten legs with erect posture flexion/extension (knee & ankle)
spread toes abduction (toes)
point toes plantar flexion (ankle)
duckwalk with buttocks on heals - this tests all lower limb and hip ROM point feet
outwards/inwards eversion/inversion (foot)
Electromyography
Electromyography is a technique for evaluating and recording the electrical
activity produced by skeletal muscles. EMG is performed using an instrument
called an electromyograph, to produce a record called an electromyogram. An
electromyograph detects the electrical potential generated by muscle cells when
these cells are electrically or neurologically activated. The signals can be
analyzed to detect medical abnormalities, activation level, recruitment order or
to analyze the biomechanics of human or animal movement.
There are two kinds of EMG
i. surface EMG
ii. intramuscular (needle and fine-wire) EMG
To perform intramuscular EMG,
i. a needle electrode or a needle containing two fine-wire electrodes is
inserted through the skin into the muscle tissue.
ii. A trained professional (such as a neurologist, physiatrist, or physical
therapist) observes the electrical activity while inserting the electrode.
iii. The insertion activity provides valuable information about the state of the
muscle and its innervating nerve. Normal muscles at rest make certain,
normal electrical signals when the needle is inserted into them.
iv. Then the electrical activity when the muscle is at rest is studied.
(Abnormal spontaneous activity might indicate some nerve and/or muscle
damage. )
v. Then the patient is asked to contract the muscle smoothly.
vi. The shape, size, and frequency of the resulting motor unit potentials arejudged.
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vii. Then the electrode is retracted a few millimetres, and again the activity is
analysed until at least 1020 units have been collected.
* Each electrode track gives only a very local picture of the activity of the whole
muscle. Because skeletal muscles differ in the inner structure, the electrode has
to be placed at various locations to obtain an accurate study.
Intramuscular EMG may be considered too invasive or unnecessary in some
cases.
Instead, a surface electrode may be used to monitor the general picture of
muscle activation. This technique is used in a number of settings; for example, in
the physiotherapy clinic.
Muscle activation is monitored using surface EMG and patients have an auditory
or visual stimulus to help them know when they are activating the muscle
(biofeedback).
A motor unit is defined as one motor neuron and all of the muscle fibres it
innervates.
When a motor unit fires, the impulse (called an action potential) is carried down
the motor neuron to the muscle.
The area where the nerve contacts the muscle is called the neuromuscular
junction.
After the action potential is transmitted across the neuromuscular junction, an
action potential is produced in all of the innervated muscle fibres of that
particular motor unit.
The sum of all this electrical activity is known as a motor unit action
potential (MUAP). This electro physiologic activity from multiple motor units is
the signal typically evaluated during an EMG.
The composition of the motor unit, the number of muscle fibres per motor unit,
the metabolic type of muscle fibres and many other factors affect the shape of
the motor unit potentials in the electromyogram.
Normal results
Muscle tissue at rest is normally electrically inactive. After the electrical
activity caused by the irritation of needle insertion subsides, the
electromyograph should detect no abnormal spontaneous activity. When the
muscle is voluntarily contracted, action potentials begin to appear. As the
strength of the muscle contraction is increased, more and more muscle fibres
produce action potentials. When the muscle is fully contracted, there should
appear a disorderly group of action potentials of varying rates andamplitudes.
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Abnormal results
EMG is used to diagnose diseases that generally may be classified into one of the
following categories: neuropathies, neuromuscular junction diseases and
myopathies.
Neuropathic disease has the following defining EMG characteristics:
An action potential amplitude that is twice normal due to the increased
number of fibres per motor unit because of reinnervation of denervated
fibres
An increase in duration of the action potential
A decrease in the number of motor units in the muscle (as found
using motor unit number estimation techniques)
Myopathic disease has these defining EMG characteristics:
A decrease in duration of the action potential
A reduction in the area to amplitude ratio of the action potential
A decrease in the number of motor units in the muscle (in extremely
severe cases only)
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