Original Editor - The Open Physio project.
Introductionmuscle strength is typically performed as part of a patient's objective assessment and is an important component of the physical exam that can reveal information about neurologic deficits. It is used to evaluate weakness and can be effective in differentiating true weakness from imbalance or poor endurance. It may be referred to as motor testing, muscle strength grading, manual muscle testing, or many other synonyms. Muscle strength can be assessed by a number of methods: manually, functionally or mechanically. 
The function of muscle strength testing is to evaluate the complaint of weakness, often when there is a suspected neurologic disease or muscle imbalance/weakness. It is an important part of the assessment in many client groups including
- patients with stroke, brain injury, spinal cord injury, neuropathy, amyotrophic lateral sclerosis, and a host of other neurologic problems.
- rehabilitation after sporting injuries eg ACL repair
- after fractures and joint replacements eg TKR
- gait and balance problems in the older adult
- falls risk assessment
The Oxford Scale
- Flicker of movement
- Through full range actively with gravity counterbalanced
- Through full range actively against gravity
- Through full range actively against some resistance
- Through full range actively against strong resistance
Commonly tested muscles include the shoulder abductors, elbow flexors, elbow extensors, wrist extensors, finger flexors, hand intrinsics, hip flexors, knee extensors, dorsiflexors, great toe extensor, and plantar flexors. These muscle groups are commonly chosen, so that important spinal nerve roots are assessed systematically eg testing the strength of the elbow flexors, elbow extensors, wrist extensors, finger flexors, and hand intrinsics allow for a methodical evaluation of the C5 to T1 nerve roots.
This short mute video is a good introduction.
There are a number of limitations to the usefulness of the Oxford scale. These include:
- Poor functional relevance;
- Non-linearity i.e. the difference between grades 3 and 4 is not necessarily the same as the difference between grades 4 and 5;
- A patient's variability over time i.e. alternating between grades due to fatigue;
- Intra-rater reliability;
- Only assesses muscles when contracting concentrically;
- The difficulty of applying the Oxford Scale to all patient's in clinical practice (so that strength is rarely assessed throughout full range as many patients assessed by physiotherapists do not possess full range due to their respective pathology).
Due to these shortcomings, physiotherapists commonly use modified versions of the Oxford scale in clinical practice. 
Performing Manual Muscle Tests
The following links demonstrate Manual Muscle Testing of specific joints and movements:
- Rising from a chair or stepping onto a chair tests proximal leg strength, walking on the heels and on tiptoe tests distal strength.
- Pushing with the arms to get out of a chair indicates quadriceps weakness.
- Swinging the body to move the arms indicates shoulder girdle weakness.
- Rising from the supine position by turning prone, kneeling, and using the hands to climb up the thighs and slowly push erect (Gowers sign and seen in Duchenne gait) suggests pelvic girdle weakness.
Muscle strength testing can help diagnose many problems in which weakness is a plays a role. Careful technique is important for ensuring valid and reproducible results. The Oxford Scale is commonly accepted and does not require special equipment, and demonstrates reasonable interrater reliability. More precise methods of measurement, such as hand-grip dynamometry, are less subjective and provide a quantifiable measurement that can be tracked over time. However, a cross-sectional study (2020) shows a lower correlation between the handgrip strength and standard strength measures of the lower limbs (hip, knee, and ankle extensor/flexor muscles), and functional capacity in older women. Functional assessment of strength focuses on how independently patients are able to perform their activities of daily living and whether strength is a limiting factor.
- Naqvi U. Muscle strength grading. InStatpearls [Internet] 2019 May 29. StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK436008/ (last accessed 7.1.20)
- Vibro56 MMT Available from:https://www.youtube.com/watch?v=gDFhiVCMPm8&t=15s (last accessed 19.12.2019)
- Cuthbert SC, Goodheart GJ. On the reliability and validity of manual muscle testing: a literature review. Chiropractic & Osteopathy 2007; 15:4
- Porter S. Tidy's Physiotherapy. Edinburgh: Churchill Livingstone, 2013.
- Merck Manual How to assess muscle Strength. Feb 2018 Available from:https://www.merckmanuals.com/professional/neurologic-disorders/neurologic-examination/how-to-assess-muscle-strength (last accessed 7.1.2020)
- Rodacki AL, Moreira NB, Pitta A, Wolf R, Melo Filho J, Rodacki CD, Pereira G. Is Handgrip Strength a Useful Measure to Evaluate Lower Limb Strength and Functional Performance in Older Women?. Clinical Interventions in Aging. 2020;15:1045.