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Manual muscle strength testing has been around at least since 1915 with over 6 textbooks on the topic currently in publication. Let’s first define exactly what we are talking about when we describe manual muscle strength testing for this article.
Muscle testing falls broadly into 2 major categories. One category uses testing to measure strength based upon the functional capacity of the muscle and the directly affiliated nerves. The other category utilizes muscle testing as a method of gaining insights into remote areas of the body or even other people. This article is addressing the first category of measuring direct muscle strength.
Muscle testing may be done using equipment, manual methods or a hybrid of the two. State of the art testing where documentation is required for insurance or legal cases typically involves sophisticated equipment (i.e. Cybex, Biodex). While muscle strength testing with this type of equipment can be extremely accurate, it tends to be limited in the number of different muscles that can be measured and takes extensive amounts of time and money to perform.
Manual muscle testing for strength utilizes the examiner’s senses to evaluate how much strength the subject is capable of producing with each test. Accuracy suffers to some degree because of this and results are recorded in a semi-quantative manner (i.e. 0-100%) rather than in pounds of force. On the plus side, manual testing offers a much broader range of muscles that can be measured and can be done in a much quicker time frame and lower cost.
Hybrid systems utilize devices that the examiner holds in their hand to measure the peak force that subjects can exert with their muscles. These hybrid systems are somewhere in between the sophisticated systems and purely manual methods regarding the number of different muscles that can be tested and the accuracy of the results, time and cost.
Cuthbert & Goodheart did a peer reviewed, nationally indexed study of over 100 research articles done on purely manual muscle testing methods. There findings concluded that there was “good reliability and validity in the use of MMT [manual muscle testing] for patients with neuromusculoskeletal dysfunction. The observational cohort studies demonstrated good external and internal validity, and the 12 randomized controlled trials (RCTs) that were reviewed show that MMT findings were not dependent upon examiner bias.” (1)
More recently (2010), Fan and others, did a study on inter-rater reliability of manual muscle strength testing for intensive care patients. They found “MMT has excellent inter-rater reliability in trained examiners and is a reliable method of comprehensively assessing muscle strength.” (2)
In 2000, Gregson found that using the Medical Research Council scale for manual muscle strength testing provided reliable results for all muscle groups tested. (3)
3 – Gregson JM. Reliability of measurements of muscle tone and muscle power in stroke patients. Age Ageing. 2000;29:223–228