Testing Muscular Strength

How strong are you? Your answer depends, in part, on the type of strength test you take. Strength is measured with isometric, isokinetic, and isotonic tests.

Isometric strength is measured with instruments such as the grip dynamometer, which measures the force of your grip, or the cable tensiometer, which measures the strength of most muscle groups. In an isometric contraction the muscle does not shorten (isometric means "constant length") even though the person is exerting maximal force. Isometric strength varies with the angle of the joint and does not provide a measure of strength throughout the normal range of motion of a joint.

Isokinetic strength is measured with a special machine that controls the speed at which you can move a joint through its range of motion. A limb, such as the lower leg, is attached to a lever arm that controls how fast the limb moves. When a muscle contracts with as much force as possible to move the limb, sensors in the machine monitor force throughout the range of motion. These machines are expensive and can usually be found in physical therapy and athletic training facilities.

Isotonic (dynamic) strength is the most familiar type of strength measure. Strength is simply measured as the heaviest weight lifted through a normal range of motion using either a barbell or a machine.

The greatest weight you can lift in good form through a joint's range of motion is called the one-repetition maximum, or 1-RM, and is a measure of maximal muscle strength. To measure your 1-RM, you are asked to lift a weight you think you can lift and then lift increasingly heavier weights only once each until you get to a weight you cannot lift. The last weight lifted in good form is your 1-RM. Some fitness facilities measure the 3-RM or 5-RM because it requires a less intense effort.