MANUAL MUSCLE TESTING

 

MANUAL MUSCLE TESTING

Manual muscle testing is an integral part of the shoulder physical examination and provides useful information in the treatment of shoulder disorders. Several textbooks on manual muscle testing techniques have been published. To master manual muscle testing, the physician must practice and be meticulous with patient positioning and stabilization.

Manual muscle testing positions have generally been based on anatomical knowledge of the origins and insertions of the muscles and the anticipated action of the muscles. Electromyography (EMG) analysis has been used in studies to quantify muscle activity during manual muscle testing and exercise. Ideally, a muscle test would create a maximum amplitude in the EMG for the target muscle, with minimal activity in the synergistic muscles. Where available, this discussion includes published EMG data that is relevant to manual muscle testing. Researchers have shown that the reliability of manual muscle test evaluators and intervalutators is high in identifying a degree of strength when evaluated on a numerical scale. However, manual muscle testing remains problematic because muscle strength can vary widely within muscle grades. Many times, significant weakness must be present before it can be detected. In large muscle groups, patients with up to 50% absolute loss of strength relative to the normal limb, as measured by dynamometry, are often classified as normal by manual muscle testing. Agre and Rodríguez found that muscles producing forces up to 8% of the opposite normal limb were rated good (4/5) during a manual muscle test. Other researchers found that dynamometer measurements detected increases in strength over time, with no change in manual muscle test scores. Since manual muscle testing does not provide accurate objective measurements of strength deficits, the use of a portable dynamometer is recommended during manual shoulder muscle testing. Dynamometric data can provide objective measures of strength (strength) when limbs are compared or as a measure of strengthening progress during rehabilitation. Most studies have found high levels of intra-examiner reliability in portable dynamometer tests. An examiner inexperienced in using a portable dynamometer may wish to perform a muscle test with and without the dynamometer. When the dynamometer comes between the examiner and the subject, it can reduce the examiner's sensitivity. Another consideration is that the isometric grip during manual muscle testing should be maintained for at least 4 seconds to allow for maximum tension development. Longer retention can reveal undetectable weakness with 1 to 2 second retention. Testing a muscle in both a shortened and a stretched position can be important because the length of the muscle at the time of the exam can affect the force produced by the muscle. A muscle held in a chronically stretched position due to postural habits or other reasons may be weak in a shortened position but may be strong in a more stretched position. This result reflects a change in the normal length-stress curve. Other muscles weaken anywhere in the range of motion due to disuse atrophy. Whether the muscle is tested in a shortened position or in a stretched position, the clinician receives valuable information by developing a corrective strengthening program.

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