Muscle function/strength
What is muscle weakness?
a loss of force-generating ability of the muscles.
May be secondary to:
- Immobilisation of joints, muscles and connective tissue
- Disuse
- Disorders of brain, nerve, muscle, joints and connective tissue
Muscle strength decreases most during the first week of immobilisation; little further weakening occurs later on
What are contraindications to assessing muscle strengh?
Region of a dislocation or unhealed fracture.
Immediately after surgery if motion to the part will interrupt the healing process.
Risk of further injury
Pain: inhibition of muscles and therefore inaccurate assessment
How is muscle function assessed?
• Assess/measure weakness/strength in physical examination.
• Interpret lack of strength or no strength meaning, develop a provisional diagnosis.
• Plan to change it, monitor it or ignore it with respect to the patient’s goals and expectations.
• Intervene weakness by doing a strengthening intervention if appropriate.
• Assess/measure strength again and evaluate the change in measurement of strength, plan to progress/change/improve your intervention
What is manual testing?
putting hands on patient and feeling their resistance isometrically or thru range
What is the protocol for 1RM testing?
--> the maximal weight an individual can lift for only one repetition w/ correct technique.
Purpose: assessing the strength capacity of an individual
Test procedure:
1. warm-up using submaximal repetitions.
2. Select initial weight that is within the subject’s perceived
capacity (~50%–70% of capacity).
3.Resistance is progressively increased until the subject cannot
complete the selected repetition.
4. Determine the 1-RM within four trials with rest periods of 3 to
5 minutes between trials. (The final weight lifted successfully is
recorded as the 1 RM)
What is muscle atrophy?
--> loss of skeletal muscle mass
• changes in the EMG but also reduced muscle weight and size of muscle fibres
• Slow muscle fibres (w/ predominantly oxidative metabolism) are most susceptible to atrophy
• decreased rate of protein synthesis & increased protein breakdown
• oxygen supply to disused muscle may also be impaired
• loss of mitochondrial function during the first days of disuse
• complete or near complete recovery from atrophy is possible but recovery phase is much longer than the total immobilisation period
What are the precautions for assessing muscle strength?
History or risk of cardiovascular problems, for
example aneurysms, hypertension, angina,
myocardial infarctions
Abdominal surgery, pregnancy or immediate post-natal period
Fatigue may be detrimental or exacerbate
condition (e.g. malignancy, multiple sclerosis,
neuromuscular diseases).
Osteoporosis or bone fragility.
Instability, hypermobility or subluxed joint/s.
Painful conditions where assessment may
aggravate.
What factors affect muscle function and strength?
• Age (strength tends to peak between 30-25yrs)
• Gender: men > women
• Muscle size: small = less tension
• Speed of contraction: moderate pace
• Previous training effect: good instructions and allow practice.
• Joint position (strongest at midrange, weaker at extremes of range)
• Temperature
• Fatigue
• Patient : motivation, pain etc
What is a hand held dynamometer?
is more objective, measures how much force is exerted
What is the Oxford Scale?
• The Oxford Muscle Scale is a numerical rating scale used to quantify the power or strength produced
by the contraction of a muscle.
• Tested through range
• Consider the effects of gravity
• Uses: Manual Assessment of muscle strength in musculoskeletal or neurological conditions
0/5 No contraction
1/5 Visible/palpable muscle contraction but no movement
2/5 Movement with gravity eliminated
3/5 Movement against gravity only
4/5 Movement against gravity with some resistance
5/5 Movement against gravity with full resistance
What are other causes of muscle weakness/atrophy?
• aging
• malnutrition • fatigue • muscle & tendon injuries
• many injuries or diseases that of musculoskeletal or
nervous system • Pain inhibition
What are common trick or substitute movements?
aka compromising
Direct or indirect substitution
- Another prime mover, for example: no supinator, biceps brachii supinate and elbow flexion.
- Fixator muscles produce movement, for example: hip abductor weak, lateral abdominals may elevate the pelvis.
What is muscle activation?
How much you are able to recruit and activate motor units
evaluated through observation or palpation, or via surface or indwelling EMG
What is a grip strength dynamometer?
objective measurement of muscle strength
What is RISOM?
• Resisted isometric muscle contraction
• In mid-range, no movement at the joint and no trick
movements
• Patient is instructed to exert maximal effort
• Ask patient for pain/symptoms
• Not able to detect small differences in strength => use
dynamometer for greater accuracy
What is the difference between muscle strength and muscle endurance?
strength : the ability to exert force on an external resistance
endurance : the ability of a given muscle to exert force against a load, consistently and repetitively , over a period of time, ie. repetitions to fatigue/failure
What is a force frame?
useful for providing a stable, supportive set up, not limited by tester strength
What do RISOM results mean?
• Strong and Painless: No lesion in the contractile structure
• Strong and Painful: Minor lesion in a part of the muscle or tendon and its
attachment.
• Weak and Painless: There could be a complete rupture of the muscle or tendon or
impaired neural function, including deconditioning (for longer standing issues) or pain
inhibition.
• Weak and Painful: Pain inhibition OR patient is reluctant to reproduce pain OR could
also indicate a more significant injury
What is functional assessment?
functional task relevant to the client, ie. related to day to day activity, work or sport
What is the protocol for strength testing?
• No clothes to inhibit movement.
• Clear instruction.
• Test unaffected side first.
• Same patient position.
• Same therapist position.
• Same joint position.
• Standardised instructions and encouragement.
• Stabile proximal segment (patients’ body weight, position or external devices).
• Stop trick/compensatory movements.
• Use same landmarks for dynamometer placement
• Use same device
• Use same units of measure
• Record best of 3 reps (take the highest measure)