Active Resistance Test

An alternative to the break test is the application of manual resistance against an actively contracting muscle or muscle group (i.e., against the direction of the movement as if to prevent that movement). This may be called an “active resistance” test. During the motion, the therapist gradually increases the amount of manual resistance until it reaches the maximal level the patient can tolerate and motion ceases. This kind of manual muscle test requires considerable skill and experience to perform and is so often equivocal that its use is not recommended.

Application of Resistance

The principles of manual muscle testing presented here and in all published sources since 1921 follow the basic tenets of muscle length–tension relationships as well as those of joint mechanics.1,2 In the case of the biceps brachii, for example, when the elbow is straight, the biceps lever is short; leverage increases as the elbow flexes and becomes maximal (most efficient) at 90°, but as flexion continues beyond that point, the lever arm again decreases in length and efficiency.

In manual muscle testing, external force (resistance) is applied at the end of the range in one-joint muscles to allow for consistency of procedure. Two-joint muscles are typically tested in mid-range where length-tension is more favorable. Ideally, all muscles and muscle groups should be tested at optimal length-tension, but there are many occasions in manual muscle testing where the therapist is not able to distinguish between Grade 5 and 4 without putting the patient at a mechanical disadvantage. Thus, the one-joint brachialis, hip abductors, and quadriceps muscles are tested at end range and the two-joint hamstrings and gastrocnemius muscles are tested in mid-range.

The point on an extremity, or part, where the therapist should apply resistance is near the distal end of the segment to which the muscle attaches. There are two common exceptions to this rule: the hip abductors and the scapular muscles. In the patient who has an unstable knee, resistance to the hip abductors should be applied at the distal femur just above the knee. When using the short lever, hip abductor strength must be graded no better than Grade 4 even when the muscle takes maximal resistance. However, in testing a patient with Grade 5 knee strength and joint integrity, the therapist should apply resistance at the ankle; the longer lever provided by resistance at the ankle is a greater challenge for the hip abductors and is more indicative of the functional demands required in gait. It follows that when a patient cannot tolerate maximal resistance at the ankle, the muscle cannot be considered Grade 5.

An example of testing with a short lever occurs in the patient with an above-knee amputation, where the grade awarded, even when the patient can hold against maximal resistance, is Grade 4. Because the weight of the leg is so reduced and the therapist’s lever arm for resistance application is so short, patients can easily give the impression of a false Grade 5 yet may struggle with the force demands of a prosthesis in the real world. The muscular force available should not be overestimated in predicting a patient’s functional ability in any circumstances such as age or disability.

In testing the vertebroscapular muscles (e.g., rhomboids), the preferred point of resistance is on the arm rather than on the scapula where these muscles insert. The longer lever more closely reflects the functional demands that incorporate the weight of the arm. Other exceptions to the general rule of applying distal resistance include a painful condition to be avoided or a healing wound in a place where resistance might otherwise be given.

The application of manual resistance should never be sudden or uneven (jerky). The therapist should apply resistance with full patient awareness in a somewhat slow and gradual manner, slightly exceeding the muscle’s force as it builds over 2-3 seconds to achieve the maximum tolerable force intensity. Applying resistance that slightly exceeds the muscle’s force generation will more likely encourage a maximum effort and an accurate break test. Critical to the accuracy of a manual muscle test is the location of the resistance and the consistency of application across all patients. (The therapist should make a note of the point of resistance, if a variation is used, to ensure consistency in testing).

The application of resistance permits an assessment of muscular strength when it is applied in the direction opposite the muscular force or torque. The therapist also should understand that the weight of the limb plus the influence of gravity is part of test response. When the muscle contracts in a parallel direction to the line of gravity, it is noted as “gravity minimal.” It is suggested that the commonly used term “gravity eliminated” be avoided because, of course, that can never occur except in a zero-gravity environment. Thus, weakened muscles are tested in a plane horizontal to the direction of gravity; the body part is supported on a smooth, flat surface in such a way that friction force is minimal (Grades 2, 1, and 0). A powder board may be used to minimize friction. For stronger muscles that can complete a full range of motion in a direction against the pull of gravity (Grade 3), resistance is applied perpendicular to the line of gravity (Grades 4 and 5). Acceptable variations to antigravity and gravity-minimal positions are discussed in individual test sections.

The Grade 5 (Normal) Muscle

The wide range of “normal” muscle performance leads to a considerable underestimation of a muscle’s capability. If the therapist has no experience in examining persons who are free of disease or injury, it is unlikely that there will be any realistic judgment of what is Grade 5 and how much normality can vary. Generally, a student learns manual muscle testing by practicing on classmates, but this provides only minimal experience compared to what is needed to master the skill. It should be recognized, for example, that the average therapist cannot “break” knee extension in a reasonably fit young man, even by doing a handstand on his leg!

The therapist should test “normal” muscles at every opportunity, especially when testing the contralateral limb in a patient with a unilateral problem. In almost every instance when the therapist cannot break the patient’s hold position when applying maximum resistance, a grade of 5 is assigned. A grade of 5 must be accompanied by the ability to complete full range of motion or maintain end-point range against maximal resistance.