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Muscle Strength Measurement

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Updated July 17, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Dynamometer Hand Grip Strength Test
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If you are having pain or difficulty with normal movement, your doctor may refer you to physical therapy for treatment. You may also choose to attend physical therapy through self-referral if your state allows direct access.

Your physical therapy plan typically starts with an evaluation, during which your physical therapist will collect information and data to help make a diagnosis and customize the best treatment strategy for your condition. Some of these tests may measure range of motion, gait, flexibility, balance, mobility and strength.

What Is Strength?

Strength is the ability of your muscle(s) to contract and produce force. A lot of things can limit muscle strength, such as surgery, illness or injury. Lack of physical exercise can also decrease your strength, which can lead to repetitive strain injuries.

How Is Strength Measured?

Manual muscle-testing and the use of a dynamometer are the most common methods to measure strength.

Manual Muscle-Testing

This is the most popular strength test. Your physical therapist will push on your body in specific directions while you resist the pressure. A score or grade is then assigned, depending on how much you were able to resist the pressure. Strength is measured on a five-point scale:

0/5. A 0/5 score means that you are unable to create any visible or noticeable contraction in a specific muscle. This occurs 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 at all.

1/5. A grade of 1/5 occurs when muscle contraction is noted but no movement occurs. The muscle is not strong enough to lift the particular body part against gravity or move it when in a gravity-reduced position.

2/5. This muscle-strength grade is assigned when your muscle can contract but cannot move the body part fully against gravity. When gravity is reduced or eliminated during a change in body position, the muscle is able to move the body part through its full range of motion.

3/5. A 3/5 grade means that you are able to fully contract your muscle and move your 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. A 4/5 grade indicates that the muscle yields to maximum resistance. The muscle is able to contract and provide some resistance, but when your physical therapist presses on the body part, the muscle is unable to maintain the contraction.

5/5. This means the muscle is functioning normally and is able to maintain its position even when maximum resistance is applied.

Occasionally your physical therapist may grade your muscle strength in half increments, using the + or - sign. A grade of 4+/5 indicates that your muscle yielded to maximum resistance, but was able to provide some resistance during the testing. A 4-/5 grade means that your muscle was not able to provide much resistance at all during testing. The use of these incremental grades is subjective, which makes them unreliable.

Manual muscle-testing is popular because it is inexpensive and readily available. The method cannot detect small changes in strength that may occur as you work hard in physical therapy to improve your condition.

Dynamometer Testing

Another method to measure strength is by using a device called a dynamometer. Your physical therapist will hold the dynamometer as you press it. The device will electronically display the amount of force you are exerting in pounds or kilograms. Smaller, handheld dynamometers can measure grip strength; even smaller pinch-grip dynamometers can measure your pinch strength.

A dynamometer can test for small changes in your ability to contract a specific muscle or muscle group. One limitation, however, is that the standard device can be quite expensive and bulky, making it difficult to use in the home-care setting.

Bottom Line:

Strength measurements can help your physical therapist determine the cause of your problem and devise an effective treatment plan. Increasing your strength during physical therapy can lead to real functional improvements in your health.

O'Sullivan, S. B., & Schmitz, T. (1994). Physical rehabilitation, assessment and treatment. (3 ed.). Philadelphia: F. A. Davis Company.

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