Victor Forge
Muscle strength testing is an important component of the physical exam that can reveal information about neurologic deficits and help diagnose many problems in which weakness plays a role. It is used to evaluate the complaint of weakness, often when there is a suspected neurologic disease or muscle imbalance/weakness. Muscle strength can be assessed by a number of methods, including manual muscle testing, which involves testing key muscles from the upper and lower extremities against the examiner's resistance and grading the patient's strength on a scale of 0 to 5. Other methods include dynamometry, which uses a handheld device to measure muscle strength, and isokinetic, isotonic, and isometric testing.
| Characteristics | Values |
|---|---|
| Purpose | To evaluate the complaint of weakness, often when there is a suspected neurologic disease or muscle imbalance/weakness |
| Muscle groups tested | Shoulder abductors, elbow flexors, elbow extensors, wrist extensors, finger flexors, hand intrinsics, hip flexors, knee extensors, dorsiflexors, great toe extensor, and plantar flexors |
| Muscle strength grading scale | 0 to 5 |
| Testing methods | Isokinetic, isotonic, and isometric testing; manual muscle testing; active resistance test; break test; dynamometry |
| Examiner's role | Apply resistance to the patient's muscle group, grade the patient's strength, and stabilize the joint |
| Patient's role | Push against the examiner's resistance, exert pressure during dynamometry |
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What You'll Learn
Manual muscle testing
During MMT, each muscle group is tested bilaterally. The examiner applies resistance or palpates the muscle or tendon for contraction, while the other hand stabilizes the extremity being tested to keep it in the test position. The examiner stands on the side being tested, and the patient is sitting upright with the joint positioned to allow full movement against gravity. The examiner demonstrates the desired movement, then requests the patient to repeat the motion. If the patient can move through the desired range of motion against gravity, the examiner attempts to apply resistance in the testing position. If the patient cannot move against gravity, the extremity is repositioned to allow movement with gravity eliminated.
MMT can also be performed using a handheld dynamometer, which provides a more precise and objective measurement of the force a muscle can exert. This method uses the same positioning as MMT but provides more quantifiable data. Dynamometry allows for the comparison of strength on each side and the measurement of strength changes during a rehabilitation programme.
There are various scales available for completing MMT, including the Oxford Scale (or Medical Research Council Manual Muscle Testing scale), which is the most commonly accepted method. This scale involves testing key muscles from the upper and lower extremities against the examiner's resistance and grading the patient's strength on a scale from 0 to 5. Commonly tested muscles include the shoulder abductors, elbow flexors, wrist extensors, and hip flexors.
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Active resistance testing
During active resistance testing, the patient tries to stop the therapist from "breaking" the muscle hold when resistance is applied. The therapist applies resistance to the body part at or near the end of the available range or at the point in the range where the muscle is most challenged. This test is called the break test.
The patient needs to be in a stable position, with the joint that the muscle acts on firmly fixed in place. The therapist's hand placement on the patient's limb provides additional stabilization of the proximal joints while the resistance is placed distally. One-joint muscles require resistance at the end of the range, while two-joint muscles require resistance in the mid-range as length-tension is more favorable.
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Dynamometry
Hand-held dynamometry (HHD) is a common form of dynamometry, where a therapist uses a hand-held dynamometer to assess muscle strength. The dynamometer is equipped with a small screen that displays the recorded static force in units of kgf, lb, or N. The dynamometer is held stationary by the therapist, while the patient exerts a maximum isometric force against it. Verbal commands are often given to the patient, such as "push as hard as possible," to encourage maximum effort. Each trial is performed over a 3-4 second hold, with 2-3 trials per session.
HHD has been shown to have good to excellent test-retest reliability for strength testing in various muscle groups, including the shoulder, elbow, wrist, hip, and ankle. It is also a valid and reliable measure of muscle strength in healthy adults, with moderate concurrent validity when compared to the "gold standard" measure of isokinetic dynamometry (IKD) for peak torque values in hip extension.
However, there are some limitations to dynamometry. Firstly, it can only test a limited number of extremity muscles, and proper calibration of the instrument is essential. Additionally, the examiner may not be strong enough to provide counterbalance when testing certain lower extremity muscles. Dynamometers are also expensive and not always available in all settings.
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Isokinetic testing
The test should not cause any pain or discomfort, and the patient should be appropriately positioned and warmed up before beginning the test. The patient will be asked to perform a set of exercises to warm up their muscles before getting into the machine for testing. The physiotherapist will then explain how the machine works and allow the patient to become familiar with it before starting the test.
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Isotonic and isometric testing
Muscle strength testing is used to determine the capability of a muscle or muscle group to produce force. It is an important component of the physical exam that can reveal information about neurologic deficits and is used to evaluate weakness. It can be used to diagnose many problems in which weakness plays a role, including suspected neurologic disease, muscle imbalance, or weakness. It is also used in the rehabilitation community to assess the progress of patients undergoing rehabilitation for injuries.
Isotonic contractions may be more effective than isokinetic contractions in developing muscle strength. However, a study found low correlations between isokinetic, isotonic, and isometric strength measurements of athletes' strength at the time of measurement. Isometric testing may be preferable to isotonic testing for patients with knee pain, as it was associated with lower knee pain intensity.
Manual muscle testing is another method of assessing muscle strength. This can be done through the break test, where resistance is applied to the body part at or near the end of the available range, or the active resistance test, where resistance is applied through the available range of motion. Dynamometry is a more precise and objective measurement of the force a muscle can exert, allowing for the comparison of strength on each side.
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Frequently asked questions
Muscle strength testing is used to determine the capability of a muscle or muscle group to produce force. It is an important component of the physical exam that can reveal information about neurologic deficits. It is also used to evaluate weakness and can be effective in differentiating true weakness from imbalance or poor endurance.
There are three key approaches described in the literature and used clinically: isokinetic, isotonic, and isometric testing. Manual muscle testing helps to determine the extent and degree of muscle weakness resulting from disease, injury or disuse. Other types of testing include active resistance testing and dynamometry.
Muscle strength is graded on a scale of 0 to 5 in relation to the expected strength for a muscle. The Medical Research Council Manual Muscle Testing Scale (or MRC scale) is one of the more common methods, where the provider pushes parts of your body in specific directions while you push back against the pressure.
