Muscle testing
Muscle testing is a skill learned early in a physical therapist's training. As part of the objective exam, muscle testing provides insight into the health and functional capabilities of a given muscle or muscle group.
Summary
- Muscle testing is a crucial skill for physical therapists, helping assess muscle health, diagnose impairments, and guide treatment plans through objective strength evaluations.
- Various muscle strength assessment methods exist, including the Oxford Scale, Kendall Muscle Grading System, and Daniels and Worthingham’s Scale, each with its strengths and limitations, particularly in interrater reliability and measurement of eccentric strength.
- Functional strength tests and technology-enhanced assessments like break testing, dynamometry, and standardized functional tasks (e.g., 30s Chair Stand Test) provide additional insights into muscle performance beyond traditional manual muscle testing.
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Therapists can perform muscle testing on individual muscles and functional muscle groups, or they can do so based on myotomes. Results of muscle strength testing can provide insight into causative factors for an injury or pain, explain reports of functional impairments, and help guide a treatment plan.
There are few patient populations for which some kind of muscle strength assessment is not beneficial, so having a reliable, evidence-based, and standardized method for assessing strength is important. This article will explore different types of muscle strength assessments, safety considerations, and how to make the most of the information.
How is muscle testing done?
Several options are available when it comes to muscle testing.
Oxford Scale (AKA Medical Research Council Manual Muscle Testing Scale)
The Oxford Scale is considered the most commonly accepted method for evaluating muscle strength.
To administer this scale, examiners target critical upper and lower extremity muscles and grade it on a 0-5 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
Some limitations to this scale include the fact that there can be a significant difference in the strength interval between a 3 and 4 out of 5 compared to a 4 and 5 out of 5. Similarly, interrater reliability is always an issue with manual muscle testing, especially in the four versus five scores. Finally, with this type of testing, physical therapists are only measuring concentric contractions and may miss issues in eccentric strength or muscle endurance.
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The Kendall Muscle Grading System
The Kendall Muscle Grading System is similar to the Oxford System; however, it adds plusses and minuses to increase the number of available grades. Many PT students learn this version in school. Interrater reliability can be a limitation of this system. It also only measures concentric contractions and may miss eccentric strength or muscle endurance issues.
Description | Name | Grade | |
|---|---|---|---|
No movement | No contraction felt or seen in the muscle | Zero | 0 |
No movement | Tendon becomes prominent or feeble contraction felt in muscle with no visible movement | Trace | 1 |
Supported in horizontal plane | Movement through a partial range of motion | Poor- | 2- |
Supported in horizontal plane | Movement through complete range of motion for the muscle being tested | Poor | 2 |
Supported in horizontal plane | Holds against slight pressure in test position | Poor+ | 2+ |
Tested in an antigravity position | Moves through partial range of motion against gravity | Poor+ | 2+ |
Tested in an antigravity position | Gradual release from test position occurs | Fair- | 3- |
Tested in an antigravity position | Holds test position (no added pressure) | Fair | 3 |
Tested in an antigravity position | Holds test position against slight pressure | Fair+ | 3+ |
Tested in an antigravity position | Holds test position against slight to moderate pressure | Good- | 4- |
Tested in an antigravity position | Holds test position against moderate pressure | Good | 4 |
Tested in an antigravity position | Holds test position against moderate to strong pressure | Good+ | 4+ |
Tested in an antigravity position | Holds test position against strong pressure | Normal | 5 |
Daniels and Worthingham’s Muscle Grading Scale
Similar to Kendall, this scale adds plusses and minuses to increase the number of available grades. Interrater reliability can be a limitation of this system. It also only measures concentric contractions and may miss issues in eccentric strength or muscle endurance.
Grade | Description |
|---|---|
0 | Complete lack of voluntary muscle contraction. The examiner is unable to feel or see any muscle contraction |
1 | Faint or “flicker” muscle contraction without any movement of the limb. The examiner can see or palpate some contractile activity of the muscle/s or may be able to see or feel the tendon “pop up” or tense as the person tries to perform the contraction |
2- | Gravity eliminated movement that is less than full range of motion |
2 | Very weak muscle contraction with movement through complete range of motion in a position that eliminates or minimizes the force of gravity |
2+ | In gravity minimized position, completes full available range and holds end position against mild resistance; or against gravity, completes up to half of the full range of motion |
3- | Against gravity, more than half but less than full range of motion. |
3 | Muscle can complete a full range of motion against only the resistance of gravity. |
3+ | Completes full range of motion against gravity, and holds end position against mild resistance. |
4 | Able to complete the full range of motion against gravity and can tolerate strong resistance without breaking the test position. The Grade 4 muscle clearly breaks with maximal resistance |
5 | Able to complete full range of motion and maintain end point range position against maximal resistance. The examiner cannot break the Athlete’s hold position. |
Break Testing
When performing a quick neurologic screen, break testing is often utilized in place of formal MMTs. Break testing involves applying moderate to high resistance to the targeted muscle group to determine how easily the joint “breaks” out of the testing position. While not graded on a 0-5 scale, break testing can help identify muscles that should be tested further or provide justification for performing a more thorough neurologic examination.
Functional Strength Testing
Functional strength testing is an important tool for assessing the overall functional capabilities of muscle groups. Functional strength testing allows the assessment of muscles as they perform a functional task and can reveal muscle performance impairments not picked up by isolated muscle strength assessments alone.
Some examples of functional muscle strength assessments include:
- 30s Chair Stand Test
- Modified 30s Chair Stand Test
- 5x Sit to Stand
- Timed Up and Go
- Walking on toes a prescribed distance
- Walking on heels a prescribed distance
- Rising from the floor
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Precautions and contraindications of muscle testing
Muscle strength assessments can be helpful tools but must be avoided in cases where injury could be caused by the application of force to the muscles, bones or superficial tissue or where the stress or strain of a maximal contraction could be dangerous.
Some conditions in which to avoid muscle strength assessments include:
- Unhealed fractures
- Postoperative restrictions
- Dislocations or unstable joints
- Severe inflammation
- Severe pain
- Hemophilia or easy bruising from blood thinners
- Severe osteoporosis
- Cognitive concerns/decreased ability to complete or understand test instructions
- Hypertension or cardiac disease
- Spasticity (not dangerous but not accurate for isolated manual muscle testing)
Integrating technology into muscle testing assessments
As technology continues to advance in the world of physical therapy, so do tools for assessing muscle strength. Dynamometry, though not necessarily new, has continued to grow in popularity, accuracy and ease of use. Unlike traditional muscle testing in which the examiner “breaks” the patient’s strength, when using a hand-held dynamometer the patient must “make” strength by applying a maximal isometric force against the dynamometer. Some dynamometers have an analog readout, others digital and newer models can even connect to Bluetooth and transmit to an app.
Some benefits of using a dynamometer are that it can decrease subjective interpretation of grades beyond 3/5 and provide a truly objective measure of strength.
Some drawbacks include that at present there are no universal, standardized positions and subjects who are stronger than their testers can overcome them and produce a concentric rather than isometric contraction.
Tips for muscle strength assessments
As with all objective testing, the goal of muscle strength testing is to identify impairments, determine if intervention is needed and guide a care plan. Muscle weakness can contribute to pain and injury, prolong recovery from surgery or injury and interfere with functional mobility. By identifying muscle weakness you have one more target for your treatment plan. Here are some tips to remember when using muscle strength assessments:
- Record the type of muscle strength assessment you used
- Note any modifications to the patient's position
- Note pain or other symptoms elicited by muscle strength testing
- Create short and long-term goals as indicated to track your progress
- Select interventions to build strength in the affected muscles
- Reassess muscle strength at regular intervals
Now that you have reviewed some of the more commonly used scales for manual muscle testing and revisited several options for functional strength testing and hand-held dynamometers, you should feel confident in your use of muscle strength assessments to help your patients get strong and improve their level of function.
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References
- Brown M, Hislop H, Avers D. Daniels and Worthingham's muscle Testing-E-Book: Techniques of manual examination and performance testing. Elsevier Health Sciences; 2013 Jan 25.
- Kendall FP, Kendall McCreary E, Geise Provance P, McIntyre Rodgers M and Romani WA. Muscles Testing and Function with Posture and Pain - Fifth Edition. Philadelphia: Lippincott Williams and Wilkins, 2005.
- Naqvi U. Muscle strength grading. InStatpearls [Internet] 2019 May 29. StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK436008
