17 - Muscle Function Flashcards
How do we asses muscle function clinically?
Manual muscle testing (structural unit)
Electromyography (EMG) and nerve conduction studies (functional unit)
How do we do manual muscle testing? What does this test?
Typically this tests groups of muscles, not an isolated muscle.
- Agonist, antagonist, and syngerists
- Planes of movement
- Types of muscle contraction
What do electromyography and nerve conduction studies test?
Detailed evaluation of muscle and nerve function/interaction.
What are agonists? What is an example?
“Primary mover”
Responsible for initiation and execution of a specific action at a joint.
Often considered as a functional muscle group: “elbow flexors” - brachalis
What are antagonists? What are synergists? Give examples of each for the group elbow flexors.
Antagonists: oppose of reverse the action of a primary mover.
-the triceps is an antagonist of the elbow flexors
Synergists: assist the prime mover in its action - biceps brachii
How do agonists and antagonists work together to facilitate joint movement? What is the purpose of this?
Reciprocal inhibition: skeletal muscles typically function in pairs for maximal muscle effifiency, speed, and control.
- agonist increases its tone in preparation for full activation
- antagonist prepares to slow down/stop intended function
The muscle pair needs to coordinate their contractions to avoid injury.
Describe the pathway of reciprocal inhibition in neurologically intact patients?
- Ia afferent enters the sp cd, synapses on the alpha motor neuron, and causes the agonist to contract
- At the same time, the other branch of the Ia afferent synapses on the Ia inhibitory interneuron which synpase on the alpha motor neuron of the antagonist, preventing contraction of that muscle group
Describe the pathway of reciprocal inhibition in neurologically compromised patients?
LAck of reciprocal inhibition (lack of descending inhibition) causes spasticity
What are the three planes of movement? Describe each.
Frontal/coronal: divides body into anterior and posterior; abduction and adduction movements occur in this plane
Sagittal: divides body into right and left; flexion and extension occur in this plane
Transverse/horizontal: divides the body into top/bottom; internal and external rotation occurs in this plane.
Do the motions for shoulder external rotation, internal rotation, extension, flexion, and posterior reach (internal rotation).
Do the motions for external and internal rotation of the hips when they are extended and when they are flexed.
Do the motion for heel inversion and eversion. Do the motion for foot supination and promation.
Supination of the foot: inversion, adduction, and plantar flexion.
Pronation of the foot: eversion, abduction, and dorsiflection.
You are seeing a 42 yo left handed male with right shoulder pain that started after a fall. His pain is in his lateral shoulder when he reahes above his head. He has some neck pain, but no numbness or tingling. What exams should be performed?
- Range of motion
- Strength
- Reflexes
- Special tests
For the mans functional muscle assessment, what are the shoulder abductors (agonists) and shoulder adductors (antagonights)?
Shoulder abductors: deltoid and supraspinatus (first 30 degrees)
Shoulder adductors: Latissimus dorsi, pec major, teres major.
How would you use planes of movement to determine the cause of a winged scapula from a shoulder injury?
Planes of movement:
Increased winging with abduction = spinal accessory/trapezius injury
More prominent winging with flexion: long thoracic nerve/serratus anterior injury
What are the two different types of contraction?
- Isotonic: muscle length changes
- Concentric, muscle shortens
- Eccentric: muscle elongates
- Isometric: muscle length remains the same
Which type of muscle contraction is capable of producing the greatest amount of force? Why is this?
Eccentric contractions
- require less metabolic energy
- with max contraction, they can generate much higher tension levels conpared to concentric contractions
- up to 50% higher
Important concent in rehab of tendinopathies because it generates more force and stimulates collagen growth.
How would you treat a 20yo runner with achilles tendinopathy?
Eccentric exercises (muscle elongates).
This is becasue the tendon is damaged and you want to stimulate collagen growth factors.
How would you treat a 75 yo male with coronary artery disease who just suffered a myocardial infarction?
Avoid isometric exercises (muscle length remains the same) because you don’t want them to increase your blood pressure and increase preload on the heart.
What types of diseases will result in an alteration of the normal recorded electrical signals and recruitment patterns? How can these be diagonsed?
Nerve compression, hereditary or acquired diseases, or myopathy.
With EMG and nerve conduction studies.
What do EMG and nerve conduction studies test?
EMG: skeletal msucle fibers (mostly type 1, slow twitch)
Nerve conduction studies: motor, sensory, and mixed nerves (standard evaluate Ia large myelinated nerve fibers(
What is the functional element of the neuromuscular system? What are the component?
The motor unit
Lower motor neuron (anterior horn cell), axon, NMJ, and muscle fibers.
What is an innervation ratio? How does this vary?
of muscle fibers that belong to a single axon (innervated by a single axon)
- Varies between muscles
Low for fine motor - extraocular muscles
High for gross motor - soleus
The higher the innervation ratio, the _____ the force generated by that motor unit. What type of muscle fibers does a single motor unit innervate?
Higher innervation ratio = greater force generated
All muscle fibers innervated by one motor unit are of the same muscle fiber.
