When a child attends a physical therapy evaluation for a developmental concern (e.g. delayed walking), an orthopedic injury (e.g. sprained ankle), or a neurological condition (e.g. cerebral palsy), the pediatric physical therapist makes important clinical observations as part of the assessment process. From standardized tests, to medical history, to visual inspection, the physical therapy examination process is multi-fold and complex. While Manual Muscle Testing (MMT) is a tried and true method of measuring strength discrepancies in orthopedic and neurological cases in adults, isolating and grading muscle strength in children can be tricky and harder to standardize across practitioners and patients.
So how do physical therapists test for muscle strength in children?
Most of the strength testing is done through observation. Instead of testing isolated muscles, physical therapists look for movements across muscle groups. To know if a baby has the proper strength to explore his environment, we look for specific muscle actions during motions done against gravity. For example, can an 8 month old baby push himself on to hands and knees? Can a 6-month-old bring his feet to his mouth? Can a 3-months-old tuck his chin when pulled from a lying position to a sitting position? What physical therapists are looking for is 1) the ability to make certain movements against gravity at appropriate stages of development, 2) symmetry between side of the body to ensure proper growth, and 3) making sure the baby isn’t just compensating for a weak body part by using another muscle group to move inefficiently.
When testing muscle power of older children, symmetry of movement and absence of compensatory patterns are still important indicators of age-appropriate strength. While the literature has not agreed on a minimum age for MMT to be used on children (the advised range is between 5-10 years of age), the general consensus is that the child should have the language and cognitive development to follow the MMT instructions. When testing isolated joint actions and muscle strength, the examiner has to apply an external force to the muscle group being tested. In young children, the levels of resistance applied must match the child’s size and weight. Just like with babies, functional tasks are a great way to test muscle strength and power in a young child, or a child with developmental difficulties. For example, being able to perform sit to stand or squat to stand without deviations would suggest appropriate muscle strength and control of lower body muscles such as the quadriceps, hamstrings, and the glutes. Being able to perform stair climbing without needing a rail or without knees buckling would suggest sufficient lower body muscle power as well.
Adolescents can be tested using the adult standardized method of manual muscle testing. Depending on the scale used, examiners can give the muscle one of 10 grades and descriptions for strength, such as poor, fair, good, normal, etc. Because MMT is a standardized process, consistency of testing is critical. Muscles are thoroughly tested in gravity-lessened and against-gravity positions. Testing of the unaffected side is also important, to attain a normal baseline for the person being tested.
For further reading on MMT grades and procedures, consult the charts listed in the references provided. Manual Muscle Testing is used by physical therapists, physiatrists, orthopedists, and neurologists alike. It is an important part of the physical examination process. While used primarily in adults, children as young has 4 years of age can be tested using this method.
Kendall, F.P., E.K. McCreary, and P.G. Provance, Muscles: Testing and Function, in Posture and Pain. 1993, Baltimore: Williams & Wilkins.
Dutton, M. Principles of Manual Muscle Testing, in Orthopedic Examination, Evaluation, and Intervention. Available at http://highered.mheducation.com/sites/0071474013/student_view0/chapter8/manuaul_muscle_testing.html. Accessed July 6th, 2014.
Palmer, M.L. and M. Epler, Principles of Examination Techniques, in Clinical Assessment Procedures in Physical Therapy, M.L. Palmer and M. Epler, Editors. 1990, JB Lippincott: Philadelphia. p. 8-36.