Muscle Strength Flashcards
Muscle strength
The highest amount of tension or force that a muscle or muscle group can voluntarily exert in one maximal effort
Neuro - maintain upright posture, everyday actions
Motor output
Central processing - receives information from periphery interpreter it, and sends commands to motor systems
Peripheral input - visual, vestibular, somatosensory, auditory
Muscle strength: structural
Size - cross sectional area
Density of muscle fibres per unit area
Efficiency of mechanical leverage over joints
Muscle strength: bio mechanical
Visco-elastic properties - tissues absorb energy during stretch which increases force of contraction
Muscle strength: neural factors
Number of motor units recruited
Frequency of motor unit recruitment
Efficiency of synergistic coordination
Muscle strength: functional
Initial length of muscle
Postural joint stability
Upper motor neurone syndrome: negative neural components
Weakness
Decreased motor control
Upper motor neurone syndrome: positive neural components
Hypertonus/ spasticity
Hyperreflexia - increased tendon reflexes
Co-activity
Spasms
Clonus
Associated reactions
Upper motor neurone syndrome: second adaptive changes
Atrophy
Increased resistance to passive movement, intrinsic biomechanical stiffness
Contractures
Lower motor neurone
Flaccid
Hypotonic
Hyporeflexic
Denervation atrophy
No babinski
Reasons for abnormal motor output
Under-active agonist - muscle weakness, secondary disuse atrophy
Over-active antagonist - increased tone and spasticity
Shortened antagonist - secondary biomechanical changes
CNS impairments and muscle weakness: first weakness
Decreased cortical output
Reduced inputs on spinal motor-neurone pool
Reduction in number and frequency motor unit recruitment
Reduced efficiency of muscle contraction
Slowness of movement
Fatigue
Disorganised motor control
CNS impairments and muscle weakness: secondary weakness
Immobility, disuse atrophy and stiffness
Reduction in cross sectional area
Reduction in density of muscle fibres per unit
Reduction in number of motor units
Immobility - shortening of opposing muscle groups
Increased resistance to contraction in agonists
Increased collagen deposits
CNS impairments and muscle weakness: pre-CNS pathology weakness
Aging
Sedentary lifestyle
Other pathologies; OA, RA, diabetes etc.
Distribution of muscle weakness
Dependent on site and extent of lesion
Everyone is different - high variability between patients
Variability in degree of weakness in muscle groups in same individual
Distal > proximal, esp intrinsic hand muscles
Range of movement
Full range - the muscle changing from a position of full stretch and contracting to a position of maximal shortness
Outer, inner and middle ranges
Greater weakness found at shorter lengths (inner) after stroke
Outer range
From a position where the muscle is on full stretch to a position half way through the full range of motion
Middle range
The position of the full range between the mid-point of the outer range and the mid-point of the inner range
Inner range
From a position halfway through the full range to a position where the muscle is fully shortened
Measuring muscle strength
Oxford grading muscle strength scale
0 - absent voluntary contraction
1 - feeble contraction (flicker) that are unable to move a joint
2 - movement with gravity eliminated
3 - movement against gravity
4 - movement against partial resistance
5 - full strength
