Przejdź do treściStrength testing helps distinguish movement limited mainly by pain from weakness caused by tendon injury, nerve dysfunction or deconditioning after immobilisation. A single strength grade is not a diagnosis, but when it is interpreted together with range of motion, sensation and the pattern of symptoms, it can substantially narrow the differential diagnosis.
It is not simply about how much weight you can lift
During the examination, the clinician asks the patient to perform a specific movement and then gradually applies resistance. By positioning the limb carefully, selected muscle groups—and the tendons and nerves that support them—can be assessed. Failure to start a movement, normal movement without resistance, and a sudden painful “give-way” response all carry different clinical information.
What can weakness mean?
- Pain-inhibited movement: the muscle and nerve may be intact, but the patient cannot generate full effort because the movement hurts.
- Tendon injury: the muscle contracts, but force is not transmitted normally to the bone.
- Nerve injury or dysfunction: weakness often follows a recognisable anatomical pattern and may be accompanied by sensory change or altered reflexes.
- Immobilisation and disuse: strength falls gradually when a limb has not been used normally, often without the sharp or electric quality of neuropathic pain.
- A problem within the joint itself: pain and restricted motion can make a true strength assessment unreliable.
For that reason, strength testing is interpreted alongside active and passive range of motion. If the examiner can move a joint farther than the patient can move it independently, the explanation may lie in pain, muscle function, tendon continuity or the nervous system rather than in fixed joint stiffness alone.
Why does an orthopaedic surgeon compare both sides?
“Normal” strength varies with age, body build, activity level, hand dominance and previous disease or surgery. The opposite limb therefore provides a useful practical reference, although it is not a perfect control because it may also be weak or previously injured. A consistent pattern across several movements is usually more informative than a small isolated side-to-side difference.
The 0–5 scale and dynamometry
In neurological examination, the Medical Research Council scale from 0 to 5 is commonly used, ranging from no visible muscle contraction to movement against substantial resistance. It is a practical ordinal scale rather than a precise force measurement. When subtle differences matter—for example during rehabilitation monitoring or athletic assessment—a handheld dynamometer may provide a more reproducible measurement, provided the testing position and method are standardised.
Why does one weak test not establish the diagnosis?
Strength testing is influenced by pain, fear of movement, fatigue, understanding of the instruction and the examiner’s own force. Manual testing is also less sensitive to small deficits in very strong patients. The result therefore needs to fit the history and the rest of the examination and, where appropriate, be supported by ultrasound, X-ray, MRI or nerve conduction studies.
When does weakness need prompt assessment?
Sudden loss of strength after an injury, inability to lift the foot or toes, a new wrist drop, rapidly progressive numbness, or weakness accompanied by a cold and pale limb requires prompt assessment. These patterns can indicate significant tendon, nerve or vascular injury and should not simply be observed for weeks without a diagnosis.
References
- Medical Research Council. Aids to the Examination of the Peripheral Nervous System. Memorandum No. 45. London: Her Majesty’s Stationery Office; 1976.
- Bohannon RW. Manual muscle testing: does it meet the standards of an adequate screening test? Clin Rehabil. 2005;19(6):662–667. DOI: 10.1191/0269215505cr873oa.
Content prepared by: Tomasz Poboży - orthopaedic surgeon.