Muscle Strength Scale in Physical Therapy

Teachers aren't the only ones who carefully follow grading systems. Physical therapists use a muscle strength grading system to define how a muscle or group of muscles is performing.

PTs commonly use the system during an initial evaluation and assessment and at regular intervals thereafter to determine a patient's progress during rehabilitation.

Measuring your muscle strength may be an important part of your rehabilitation plan, especially if the PT feels that muscle weakness is contributing to your pain and limited mobility.

This article explains what muscle strength is and the two ways to measure it: manual muscle testing and dynamometric testing.

Defining Strength

Muscle strength is defined as the ability of a muscle to tighten (contract) and produce maximum force in a single effort. Muscle strength differs from muscle endurance, which is how well a muscle can sustain repeated contractions against resistance for an extended period of time.

Both muscle strength and endurance are needed to achieve optimal physical function and mobility. Many things can interfere with this, including:

• Short- or long-term illness
• Injury
• Lack of exercise
• Malnutrition
• Motor neuron disease, disorders that affect nerve cells that send electrical messages to the muscles, Lou Gehrig's disease
• Musculoskeletal disorders, or injuries or pain in the joints, ligaments, muscles, nerves, or tendons
• Neuromuscular diseases, or those that undercut how the muscles work, such as multiple sclerosis
• Obesity
  
• Physical disability
• Severe arthritis
• Surgery

If you're referred to a PT, muscle strength will almost certainly factor in your treatment plan, no matter what ailment you may have. And chances are, muscles of all sizes will be involved.

For example, a PT may study large muscles like the biceps or hamstrings, as well as smaller muscles like those of the wrist and hand.

PTs use two methods to measure muscle strength: manual muscle testing and dynamometric testing.

Manual Muscle Testing

Manual muscle testing (MMT) is the most common way to test muscle strength. For this test, the PT pushes on the body in specific directions while you work to resist the pressure.

The PT assigns a grade that reflects how well you were able to do this. Muscle strength is measured on a five-point scale:

• 0/5: You are unable to create any noticeable contraction in a specific muscle. This can occur when a muscle is paralyzed, such as after a stroke, spinal cord injury, or cervical or lumbar radiculopathy. Sometimes, pain can prevent a muscle from contracting.
• 1/5: Muscle contraction is noted but no movement occurs. In this case, the muscle is not strong enough to lift the particular body part against gravity or move it when in a gravity-reduced position. A small contraction may be detected with palpation (physical touch) but not enough to affect movement.
• 2/5: A muscle can contract, but it cannot move the body part fully against gravity. However, when gravity is reduced or eliminated with a change in body position, the body part will be able to move through its full range of motion.
• 3/5: You are able to fully contract a muscle and move a body part through its full range of motion against the force of gravity. But when resistance is applied, the muscle is unable to maintain the contraction.
• 4/5: The muscle is able to contract and provide resistance. But when maximum resistance is exerted, the muscle is unable to maintain the contraction.
• 5/5: The muscle is functioning normally and is able to maintain its position even when maximum resistance is applied.

Occasionally, a PT may grade strength in half increments, using the + or - sign. For example, a grade of 4+/5 indicates that a muscle yielded to maximum resistance but was able to provide some resistance during the test.

A 4-/5 grade means that a muscle was not on the verge of collapse during testing.

MMT is popular because it is inexpensive, easy to perform, and does not require any special equipment.

Still, the testing method is less reliable within the good (4/5) to normal range (5/5), with results often varying between one PT and the next.

Dynamometric Testing

Dynamometry is another method of measuring muscle strength. It evaluates the length-tension relationship of the muscle. This is how much tension a muscle exerts during a muscle contraction without motion (isometric contraction) in relation to the length of a muscle.

The test is performed by placing the body part in a position where it is not influenced by gravity. A handheld device known as a dynamometer is positioned against the muscle. The patient then exerts pressure against it for several seconds. A reading in pounds or kilograms is then displayed.

The dynamometric reading is compared to the reference (expected) values for a person of your age and sex. These readings are used to track performance as you undergo physical therapy.

Summary

Muscle strength is defined as the ability of a muscle to contract and produce maximum force in a single effort.

There are two ways physical therapists can measure muscle strength. Manual muscle testing calls for a PT to push on the body while you resist pressure. The PT then grades the effort. Dynamometric testing measures the tension that a muscle exerts during an isometric contraction, or when a muscle is tensed but doesn't move.

These tests can help a therapist gauge your current status, as well as how you are improving over time.

A Word From Verywell

If you're experiencing muscle weakness resulting in the loss of functional mobility, speak with your healthcare provider about exploring the possible causes. You may be referred to an orthopedic surgeon if the cause is believed to be musculoskeletal or a neurologist if the muscle weakness is believed to be caused by a nerve disorder. Only a proper diagnosis can lead to an effective rehab plan.