ISOTONIC AND ISOMETRIC CONTRACTIONS
Based on the pattern of tension production, muscle contraction can be classified as isotonic or isometric. In isotonic contraction, the tension (tonus) developed is constant (iso, meaning equal) while the length of the muscle changes. Examples of isotonic contraction are walking, running, and skipping. There are two types of isotonic contraction—concentric and eccen-tric. In concentric contraction, the muscle shortensas in the examples given above. In eccentric contrac-tion, the muscle lengthens during contraction (i.e., the muscle tension is less than the resistance and the muscle is stretched by the resistance). An example of eccentric contraction is lowering a book on a table. The resistance developed is less than that required for lifting the book, and the book (resistance) stretches the muscle. Eccentric contractions prevent rapid changes in length that may damage muscle tissue and help absorb shock when jumping or walking.
In isometric contraction, the muscle length (metric, measure) remains the same (iso-, meaning equal), and the tension varies. A good example is trying to lift a weight when you are unable to do so. Tension devel-ops in the muscle, but the muscle does not shorten to lift the weight. Daily activity involves a combination of isotonic and isometric contractions of muscle.