Assessment of Muscle Strength Flashcards
causes of muscle weakness
Lesion or pathology affecting the nerve which innervates the muscle
- Any lesion, injury or pathology of the muscle tissue
- Disuse
- Immobilisation
example of upper motor neuron lesion CNS
stroke
example of lower motor neuron lesion PNS
peripheral nerve lesion
effects of immobilisation on muscle
Decrease; Muscle fibre size Size and number of mitochondria total muscle weight Stores of glycogen and ATP Protein synthesis Muscle tension produced all leading to atrophy
Strength
- Ability to generate force
- Capacity to exert force
- Ability to do work against resistance
factors of strength to make movement
Combined contractile forces of the muscles causing movement
• The ability to co-ordinate the agonists, antagonists and
stabiliser muscles
• The mechanical advantages of the levers
assessment of strength
cross sectional area - CT/MRI/ Tape measure
manual muscle testing - Oxford scale how much force a muscle can make
Objective measurement - isokinetics - endurance how long can you maintain force/strain gauge, dynamometry
functional assessment - 1RM
Use of assessing cross sectional area
detect muscular atrophy
MEASURED WHHEN MUSCLE IS RELAXED
predictor of mortality in some diseases e.g. COPD
Manual Muscle Testing - MMT 0
No contraction
MMT 1
Flicker or trace of contraction
MMT 2
Full range of active movement with gravity eliminated
MMT 3
Full range of active movement against gravity
MMT 4
Full range of active movement against gravity and resistance
MMT 5
Normal
Where would you position your hands to
examine the strength of the bicep muscle?
wrist and back of elbow
principles of manual resistance
- Stabilise the proximal segment (non-moving part, muscle origin)
- Resist the distal (moving) segment
- Give yourself mechanical advantage: consider the length of the lever and where your resistance is coming from
- Respond to the patient’s effort: increase your resistance gradually
Assessment of Strength of Deltoid Muscle
shoulder abduction and pressing against elbow and put hand on opposite shoulder.
limits of oxford scale
Grade 4 is not sensitive to change in strength (amount of resistance is not measured) Grade 5 (“normal strength”) is subjective
reason to use oxford scale
- Quick
- No equipment needed
- Allows assessor to get a “feel” for the muscle and observe
movement through range - Sensitive from grade 0 to the start point of grade 4
- Assessor can adjust resistance intuitively (for example, in
trying to reproduce pain) - Useful as a screening tool for strength deficits
benefits of using handheld dynamometry
Suitable for assessing strength of individuals who score Grade 4 or 5 on the Oxford Scale
• More sensitive than MMT
• Allows measurement of Maximal Isometric
Torque = Maximum Voluntary Isometric Contraction (MVIC)
limitations of dynamometry
Requires training
• If patient is very strong the tester may not be able to fully resist the patient’s effort (needs to be a “break” test)
• Isometric testing only
purpose of hand grip dynamometry
Useful predictor of physical function in aging adults
• Hand grip is fundamental to ADLs
advantages of strain gauges
- Sensitive
- Objective
- Reliable
- Can assess a large number of muscles
disadvantages of strain gauges
Time consuming
• Requires training
• Only measures isometric force
benefits of isokinetic evaluation
Mechanical measurement of muscle performance
• Objective
• Quantitative
• Isometric / concentric / eccentric
• Muscle works at constant velocity: Isokinetic
• Resistance is variable depending on muscle ability to generate force & to keep pace with selected speed
positive of isokinetic testing
- Objective, sensitive, accurate
- Controls for speed
- Calculates agonist: antagonist ratios
- Tests isometric, concentric and eccentric strength
negatives of isokinetic testing
- Isokinetic machines are expensive and bulky
- Takes a long time to test
- Limited to a small number of muscle groups
- Open-chain movement only
- Not very functional
1 repetition maximum - 1R,
the maximal weight that can be lifted once using a proper lifting technique.
why use 1RM
- Allows dynamic movement (concentric and eccentric)
- Functional and meaningful
- No expensive equipment
- Specific to exercise prescription
- Research shows it to be very reliable (Grgic et al, 2020)
- Motivating for patient
Calculating 1 RM
determining the maximum weight that the patient can lift, without failure or compensatory body movements, with good technique. (If you do this, try to get to the 1-RM within 5 attempts.)
Functional strength testing
Performance of a compound movement, such as sit to stand, heel raise, pull up or push up
functional strength testing detects
• Speed of performance (= POWER)
• Absolute repetition number (concentric / eccentric) (=
ENDURANCE)
• Sustained maximal duration trials (isometric) (= ENDURANCE)
endurance
Ability to undergo prolonged activity or to resist stresses set up as a result of prolonged activity
muscular endurance
The ability of a muscle to sustain an isometric contraction or to
continue a dynamic contraction
cardiovascular endurance
The capacity of the individual to maintain strenuous activity of a
number of muscle groups or of the whole body for a prolonged
period
fatigue
Subjective feeling of discomfort, tiredness
• Increased perception of effort
• Decrease in maximal power produced by a muscle
What is the relationship of fatigue to task failure in PNS?
Impairment of physiological processes that enable contractile proteins to generate a force
Accumulation of metabolic by-products (H+, Pi, AMP)
ATP used faster than it can be provided
What is the relationship of fatigue to task failure in CNS?
Mechanisms in the CNS which result in decreased voluntary activation
• The “central governor theory”
