Muscle Atrophy and Muscle Function

Muscle Atrophy

• Disuse atrophy develops after weeks or months of inactivity
• Neurogenic atrophy occurs rapidly (2-3 weeks) after a lower motor neuron (LMN) lesion
• Consequences of muscle atrophy include:
  • Diminished capacity of muscle for developing torque
  • Reduced passive tension
  • Loss of joint stability
  • Postural abnormality

Examination of Muscle Bulk

• Visually inspect muscle shape and symmetry
• Compare size and contour
• Measure limb girth
• Palpation at rest

Strength and Power

• In stroke patients, there is a 50% decrease in motor units of affected extremities within 2 months
• Greater loss of fast twitch fibers
• Impairments in grip strength
• Strength loss is greater in distal extremity than proximal
• Strength losses are also found in normal extremities

Examination of Strength

• Manual Muscle Testing (MMT)
• Use active vs passive restraint
• Identify substitutions
• Use hand-held dynamometers
• Use isokinetic dynamometers
• Electromyography (EMG)

Endurance

• Fatigue is a common symptom in neurological conditions such as post-polio syndrome, MS, stroke, ALS, and Duchenne muscular dystrophy
• Exhaustion limited endurance
• Overwork weakness: prolonged decrease in absolute strength and endurance due to over-activity
• Delayed-onset muscle soreness (DOMS)

Examination of Fatigue

• Identify fatigue threshold
• Use Fatigue Impact Scale (FIS)
• Use Modified Fatigue Impact Scale (MFIS)
• Use Fatigue Assessment Scale
• Use Borg Scale of Perceived Exertion

Voluntary Movement Patterns

• Synergies are functionally linked muscles that act cooperatively to produce an intended motor action
• Abnormal synergistic patterns can occur in lesions of the corticospinal tracts (e.g., stroke)

Activity-Based Task Analysis

• Break down a specific activity into its component parts to understand and evaluate the demands of the task and the performance demonstrated
• Identify activity demands and environmental demands

Taxonomy of Tasks

• ADLs (Basic)
• IADLs
• Functional mobility skills
• BADLs
• IADLs
• Functional Mobility Skills (FMS)

Passive Motion Testing

• Normal
• Hypertonic
• Hypotonic
• Slow velocity vs High velocity
• First stretch response
• Successive stretch response
• Clonus
• Clasp knife response
• Symmetry

Modified Ashworth Scale

• Most frequently used clinical method for estimation of spasticity

Special Tests

• Pendulum test
• EMG
• Myotonometry

Wartenberg Pendulum Test

• Patient is seated or lying with lower leg hanging over the end of the couch
• Examiner extends the leg to the horizontal position, while the patient is told to relax
• Leg is then released and allowed to swing freely under the action of gravity

Reflex Integrity

• Deep Tendon reflexes
• Superficial Cutaneous reflexes
• DTR (Deep Tendon Reflex) results from stimulation of stretch-sensitive IA afferents of the neuromuscular spindle producing muscle contraction
• Muscle positioned in mid-range for adequate response
• Increased in UMNL (e.g., stroke)
• Decreased in LMNL (e.g., peripheral neuropathy)

Jendrassik Maneuver

• Enhances reflexes by distracting the patient

Primitive and Tonic Reflexes

• Present during infancy
• Not recognizable in adults in pure form

Cranial Nerve Integrity

• Assess cranial nerve function