Teachers aren’t the only ones who take the grading system seriously. Physical therapists use a muscle strength grading system to define the performance of a muscle or muscle group.
PTs typically use the system during the initial assessment and assessment and periodically thereafter to determine a patient’s progress during recovery.
Measuring your muscle strength can be an important part of your rehabilitation program, especially if the PT believes that muscle weakness is causing your pain and limited mobility.
This article explains what muscle strength is and two ways to measure it: manual muscle testing and ergometric testing.
What to expect from physical therapy
Muscle strength is defined as the ability of a muscle to tighten (contract) and produce maximum force in one effort. Muscle strength differs from muscular endurance, which is the ability of a muscle to resist repeated contractions of resistance over an extended period of time.
Both muscle strength and endurance are necessary for optimal physical function and mobility. Many things can interfere with this, including:
- short-term or long-term illness
- lack of exercise
- Motor neuron disease, a disorder that affects the nerve cells that send electrical messages to the muscle, Lou Gehrig’s disease
- Musculoskeletal disorders, or injury or pain to joints, ligaments, muscles, nerves, or tendons
- neuromuscular disorders, or disorders that impair the way muscles work, such as multiple sclerosis
- Physical disability
- severe arthritis
Other tests usually done during the assessment will measure your flexibility, gait (how someone walks or runs), range of motion (how far a body part can move), balance, coordination and mobility. These preliminary results help PT track your progress during recovery.
If you are referred to PT, muscle strength will almost certainly be a factor in your treatment plan, regardless of your medical condition. In all likelihood, muscles of all sizes are involved.
For example, PT might study large muscles like the biceps or hamstrings, as well as small muscles like the wrist and hand.
PT uses two methods to measure muscle strength: manual muscle testing and ergometric testing.
Different modalities used in physical therapy
Manual muscle testing
Manual muscle testing (MMT) is the most common method of testing muscle strength. For this test, the PT pushes your body in a specific direction as you work to resist stress.
The points assigned by PT reflect your abilities in this area. Muscle strength is measured on a five-point scale:
- 0/5: You cannot produce any noticeable contractions in a particular muscle. This can occur when muscles are paralyzed, such as after a stroke, spinal cord injury, or cervical or lumbar radiculopathy. Sometimes, pain can prevent the muscle from contracting.
- 1/5: Muscle contractions are noted, but no movement. In this case, the muscle is not strong enough to lift a specific body part against gravity or move it in a position where gravity is reduced. Palpation (physical touch) may detect slight contractions, but not enough to affect movement.
- 2/5: Muscles can contract, but cannot move body parts completely against gravity. However, when gravity is reduced or eliminated with changes in body position, the body part will be able to move through its entire range of motion.
- 3/5: You are able to fully contract the muscle and move the body part against gravity through its full range of motion. But when resistance is applied, the muscle cannot sustain the contraction.
- 4/5: The muscle is able to contract and provide resistance. But when maximum resistance is applied, the muscle cannot sustain the contraction.
- 5/5: Muscles function normally and maintain their position even when maximum resistance is applied.
Although manual muscle testing relies on individual observations, the criteria and definitions are considered sufficient to produce relatively reliable results.
Occasionally, PT may use + or – signs to score intensity in half increments. For example, a grade of 4+/5 indicates that the muscle yielded to maximum resistance but was able to provide some resistance during the test.
A 4-/5 grade means that the muscle was not on the verge of collapse during the test.
MMT is popular because it is inexpensive, easy to perform, and does not require any special equipment.
Nonetheless, the test method has low reliability in the good (4/5) to normal (5/5) range, and results usually vary from one PT to the next.
How long should physical therapy last?
Ergometry is another method of measuring muscle strength. It assesses the length-tension relationship of a muscle. This is the amount of tension exerted by a muscle during a non-exercise muscle contraction (isometric contraction) relative to the length of the muscle.
The test is performed by placing the body part in a position that is not affected by gravity. Handheld devices called dynamometers rest against the muscles. The patient then applies pressure to it for a few seconds. The reading in pounds or kilograms is then displayed.
Force readings are compared to reference (expected) values for a person of your age and gender. These readings are used to track your performance while receiving physical therapy.
Muscle strength is defined as the ability of a muscle to contract and generate maximal force in one effort.
Physical therapists can measure muscle strength in two ways. Manual muscle testing requires the PT to push your body while you resist stress. The PT then scores the effort. Dynamometric tests measure the amount of tension a muscle exerts during isometric contractions, or when a muscle is tense but not moving.
These tests can help the therapist assess your current state and how you are improving over time.
How Outcomes Are Measured in Physical Therapy
If your muscle weakness is causing loss of functional mobility, discuss possible causes with your healthcare provider. If the cause is thought to be musculoskeletal, you may be referred to an orthopedic surgeon; if the muscle weakness is thought to be caused by a neurological disorder, you may be referred to an orthopaedic surgeon. Only a correct diagnosis can lead to an effective recovery plan.
Frequently Asked Questions
Who can perform muscle strength classification?
Muscle strength grading can be performed by appropriately trained healthcare providers, nurses, physical therapists, occupational therapists, chiropractors, and other healthcare providers.
When is muscle strength grading required?
Muscle strength grading is commonly used to measure muscle strength in people with known or suspected neurological disorders such as stroke. But it can be used by anyone complaining of muscle weakness to help differentiate true weakness from imbalance or endurance issues.