Muscular Fitness Basics - Measures of Strength

Building sufficient strength throughout life is important to our ability to live independently and enjoy life to the fullest. We can measure and develop strength in several ways, each of which is highly specific to how we will use strength and should dictate the mode of training and testing.
Using muscular power during movement is called dynamic strength. Dynamic strength, also called isotonic, is defined as the maximal weight that a person can lift one time. This amount is actually a measure of strength at the hardest part of the lift, usually the beginning. Because the mechanical advantage of your muscle - lever system changes, a lift such as a forearm curl becomes easier after you overcome the initial resistance and angle of pull. Dynamic strength measurements are related to performance in sport and work. Weightlifting with machines or free weights is the common form of isotonic training. (Isotonic is "same tone" because iso means "same," and tonic means "tone,")
Another measure of strength is static strength. A person demonstrates static strength by exerting maximal force against an immovable object. Also called isometric strength, it is specific to the angle at which it was trained. Static strength doesn't necessarily reflect dynamic strength or strength throughout the range of motion. You train by exerting near maximum force against an immovable object. (Metric means "length," and isometric means "same length" - the muscle doesn't change length appreciably during the contraction.)
A popular measure of strength in clinical and rehabilitation settings is isokinetic strength, which is measured with expensive electronic or hydraulic apparatus. The equipment allows the exertion of maximal force throughout the range of motion, as well as the control of the speed of contraction. Although such devices have become popular testing aids, it is not yet clear to what extent strength throughout the range of motion is related to performance. (Kinetic means "motion" or "speed," and isokinetic means "same speed." A number of sophisticated devices are available for isokinetic measurement of muscle force and power. Sports medicine specialists test knee extension and flexion strength, power and endurance and use isokinetic devices to rehabilitate athletes following knee surgery. Variable and accommodating resistance devices are used to strengthen muscles and to prevent injuries.
Athletes may use free weights, isokinetic machines, and even isometric contractions to improve performance. Keep in mind that strength is specific to the method of training, to the speed of contractions, and to the angle used in training. Therefore, to obtain an accurate assessment of the effects of training, the method of testing should be specific to the mode of training. In other words, a static strength test will not accurately measure changes from dynamic strength training or vice versa.

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