Manual Muscle Strength Testing: Validity & Reliability


Glute Med - anterior view - half bodyManual 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. This method has been used for many decades by a wide range of practitioners, trainers, therapists, etc. The other category utilizes muscle testing as a method of gaining insights into remote areas of the body, biochemistry or even other people. This second method of utilizing muscle testing is affiliated with the field of Applied Kinesiology.  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.

Research has been extensive on manual muscle strength testing (MMST) as well as technology assisted manual testing methods, a small sample is included here.  (1, 2, 3, 4, 5) These finding support the idea that MMST has good reliability and validity for patients with neuromusculoskeletal dysfunction. These studies demonstrate good external and internal validity, and 12 randomized controlled trials (RCTs)  show that MMST findings were not dependent upon examiner bias.  Accuracy results vary from a low in the 70% range variability between examiners to as high as the 90% range.

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