Muscle testing is the evaluation of contractile units, including muscles and tendons, and their ability to generate forces.
Muscle testing is indicated in any individual with suspected or actual impaired muscle performance, including strength, power, or endurance. Impairments in muscle function may result from cardiovascular, pulmonary, musculoskeletal or neuromuscular disease or disorders. Identification of specific muscles or muscle groups with impaired function provides information for appropriate intervention, which may include strengthening exercises, functional drills, bracing, or compensatory muscle use.
It is important to determine the patient's ability to withstand the force to be applied. The patient should have good cardiovascular function, be instructed against using the Valsalva maneuver, and be positioned appropriately. Care should be taken with any body part that is under movement restriction due to fracture, post-surgical, or other tissue healing.
Forms of muscle testing include manual strength testing, functional tests, and dynamometry.
Manual muscle testing
Manual muscle strength testing is a widely used form of muscle testing in the clinic. In this form of testing, the individual is asked to hold a limb or other body part at the end of its available range or at another point in its range of motion while the clinician provides manual resistance. General procedures include the following:
- The patient should be placed in a position that provides overall support to the body so that he or she can concentrate his or her effort on the part being tested.
- The part to be tested initially is placed in an antigravity position. If muscles are too weak to function against gravity, they are then tested in the horizontal plane.
- The proximal part of the area being tested should be stabilized to reduce the opportunity for compensatory action by muscles other than those being tested.
- Resistance needs to be applied directly opposite the "line of pull" of the muscles being tested.
- Gradual, not sudden, application of pressure should take place, using a long lever arm in most cases.
- Both sides should be assessed to provide a comparison, especially when one side is affected by pathology and the other is not.
Grading of muscle tests is used to determine a patient's physical therapy diagnosis and in assessing progress over time. Objective observation includes determining the patient's ability to hold a test position, move through a full range of motion, or to overcome gravity. Care must be taken in grading, however, due to the inevitable subjectivity of muscle testing. Subjective factors include the clinician's impression of how much resistance to apply and how much is tolerated. Consistent testing procedures, including accurate joint placement and prohibition of compensatory movements, allow for increased reliability in using manual muscle testing as an evaluation tool. In studies comparing manual testing and dynamometry, results show positive correlation; however, manual muscle testing is less sensitive than dynamometry.
Traditional grading has been described using either the terms "zero," "trace," "poor," "fair," "good," and "normal," or using a numerical scale from 0 through 5. When determining a grade, first determine whether or not the patient can move the body part through its full range against gravity and hold the body part in the test position. This ability results in a grade of fair, or 3, and is the most objective observation made during testing due to the consistency of gravity. A poor grade, or 2, is given when a patient is able to move the body part through its complete range of motion in the horizontal plane, that is, with the effect of gravity eliminated. A trace grade, or 1, is given when there is no visible movement through a part's range, but a slight contraction can be palpated. When there is no evidence of even a slight contraction, a grade of zero is given.
Grades above fair are assessed with the body part in the specified test position. A grade of good, or 4, denotes the ability of the patient to hold the body part in the test position against moderate pressure. A normal grade, or 5, denotes that the patient holds the body part against strong pressure by the clinician.
Pluses and minuses can be added to the above grades to further describe muscle ability, but some discourage their use because it introduces even more subjectivity to grading. In some cases, however, the use of a plus or minus grade provides important information. For example, a patient with a fair grade (3) for a muscle group may not be able to use an orthosis effectively, but if that patient achieves a fair plus (3+), he or she can withstand minimal resistance against gravity and therefore may be able to tolerate the additional weight of an orthosis. Descriptors for plus and minus grades are included in the summary of grades below:
- Normal (5): withstands strong pressure in test position.
- Good plus (4+): withstands moderate to strong pressure.
- Good (4): withstands moderate pressure.
- Good minus (4−): withstands slight to moderate pressure.
- Fair plus (3+): withstands slight pressure. Fair (3): holds test position against gravity but tolerates no additional pressure.
- Fair minus (3−): sags from test position or only moves through partial range of motion against gravity (>50% of motion).
- Poor plus (2+): moves through 50% of motion or less in antigravity position, or holds against resistance in gravity-eliminated position (horizontal plane).
- Poor (2): moves through complete range in horizontal plane.
- Poor minus (2−): moves through partial range in horizontal plane.
- Trace (1): slight contraction, but no visible movement of body part detected.
- Zero (0): complete lack of muscle contraction.
It is important to note that manual muscle grades are an ordinal level of measurement, meaning that the categories do not represent equal magnitudes. In other words, the strength required to move from zero to trace is different from the amount of strength required to move from good to normal. Therefore, manual muscle grades are not useful for arithmetical computations.
Manual muscle testing is a relatively quick and inexpensive method of evaluating strength; however, results often do not denote a person's ability to perform functional activities. In addition, a normal muscle grade does not necessarily indicate a patient's ability to return to his or her normal level of activity, especially if it includes sports participation. This ability is better tested with functional tests.
Functional muscle testing
Functional muscle testing allows for the assessment of muscles to perform components of, or entire, tasks related to daily activities. Functional tests look at the ability of muscle groups to decelerate, stabilize or accelerate movement in all three planes of motion in a measurable way. Specific tests can be chosen to look at movements at specific joints or those that are dominant in a certain plane of motion. For example, a single-leg squat provides valuable information about the quadriceps' performance. An anterior jump test provides the same type of information on a more challenging level for the patient.
Categories of functional muscle testing include the following: balance, excursion, lunge, step-up, step-down, jump and hop tests. In performing tests, patient safety is key. Clinical judgment should be used to determine when functional testing is appropriate; for example, a person with a weight-bearing restriction should not perform a balance test on that lower extremity. Testing should be done in a progressive manner; for example, a balance test should be performed before an excursion test, a straight plane lunge test before a rotational lunge test. Tests can be used to document progress by measuring distance of reach, time, degrees of excursion, etc., as appropriate to the specific test.
Isokinetic dynamometry uses a device that measures the force used in contraction of a muscle group. The device is able to apply maximal resistance at all points in the body part's range of motion at a specified speed. Isokinetic testing can be used to objectively assess strength, power and endurance. Strength is assessed using slow velocity testing to look at peak torques produced. Power testing uses fast velocity settings to look at the amount of work performed during a particular amount of time. Endurance testing looks at the patient's ability to maintain sorce output during numerous repetitions at high velocities.
|Manual muscle testing—levels of muscle performance|
|Level of performance||Definition|
|Source: Rothstein, J.M., S.H. Roy, and S.L. Wolf. The Rehabilitation Specialist's Handbook. 2nd ed. Philadelphia: F.A. Davis Co., 1998.|
|Normal||Completes full range of motion against gravity, and holds test position against strong pressure.|
|Good||Completes full range of motion against gravity, and holds test position against moderate to strong pressure.|
|Fair||Completes full range of motion against gravity, and holds test position with slight or no added pressure. There may a gradual release from test position.|
|Poor||Completes partial range of motion against gravity, and moves through complete range of motion in horizontal plane.|
|Poor-Trace||Completes partial range of motion in horizontal plane.|
No visible movement of the part, but examiner may observe or palpate contractile activity in the muscle.
|Zero||No contraction detected in the muscle.|
Advantages of isokinetic testing include the ability to maximally load the muscle throughout its range of motion; stabilization of proximal body parts to prevent substitute motions; measurement of concentric and eccentric loading; and objectivity. As in manual muscle testing, however, isokinetic testing does not necessarily provide an accurate picture of how a muscle will function during actual activities of daily living or sports. In addition, unlike manual muscle testing, it requires expensive equipment and space.
Hand-held and grip dynamometers are smaller, less expensive alternatives for measuring muscle strength in an objective manner. Information regarding force produced during a contraction such as knee extension or hand grip is displayed in units (often pounds) on a display or dial. Use of these instruments, however, is limited to the body parts they were designed to measure; i.e., a grip dynamometer is useful only for measuring grip strength.
Valsalva maneuver— Forced expiratory effort against a closed airway, usually used during strenuous effort.
Results are recorded as described above, by the use of grades or force units. Regardless of the type of muscle testing used, the results can be used to help determine specific sites of impairment, in addition to providing data for assessing progress.
Health Care Team Roles
Muscle testing is performed by physicians, especially orthopedic doctors and physiatrists, in addition to physical therapists and occupational therapists. Manual muscle testing often is an integral part of a PT or OT evaluation of muscle function. The following knowledge is required for any health care practitioner to perform an accurate test:
- location, origin and insertion of muscle(s) being tested
- direction of muscle fiber orientation
- function of muscle being tested, in addition to functions of its synergists and antagonists
- appropriate positioning for the test
- recognition of substitution or compensation by other muscles
- recognition of the effects of factors such as restricted range of motion and pain
- specific contraindications
- ability to palpate muscle contraction
- ability to modify a test due to inability to attain a certain position
- ability to communicate to the patient regarding purpose, procedures and patient requirements for the test
American Physical Therapy Association. Guide to Physical Therapist Practice. 2nd ed. Fairfax, VA: American Physical Therapy Association, 2001.
Gray, Gary W. Lower Extremity Functional Profile. Adrian, MI: Wynn Marketing, Inc., 1995.
Hislop, Helen J. and Jacqueline Montgomery. Daniels and Worthingham's Muscle Testing: Techniques of Manual Examination. 6th ed. Philadelphia: W.B. Saunders Company, 1995.
Kendall, Florence Peterson, et. al. Muscles: Testing and Function, 4th ed. Baltimore: Williams & Wilkins, 1993.
Bohannon, R.W. "Measurement of Hand Grip Strength: Manual Muscle Testing Versus Dynamometry." Physiotherapy Canada 51 (Fall 1999): 268-72.
――――――. "Measuring Knee Extensor Strength." American Journal of Physical Medicine and Rehabilitation 80 (January 2001): 13-8.