Sunday, October 7, 2012


Muscular system is very important as it can produce movement and provide protection and support for organs in the body. The unique, characteristic feature of muscle cell is the relative abundance and organization of actin and myosin filaments within the cells. These filaments are specialized for contraction. There are three muscle types present in vertebrates; namely, smooth muscles, skeletal muscles, and cardiac muscles. The contraction of cardiac and smooth muscles is, generally, involuntary while the skeletal muscle is under voluntary control. Depending on the pattern of tension production, muscle contraction can be classified as isotonic contraction and isometric contraction. Daily activities involve both isotonic and isometric contraction combinations of the muscles.

What is Isotonic Contraction?
The word ‘isotonic’ means equal tension or weight. In this contraction, the tension developed is constant while the length of the muscle changes. It involves muscle shortening and active contraction and relaxation of the muscles and occurs with movements such as walking, running, skipping etc.
Isotonic contraction can be further divided into two categories as concentric and eccentric. In concentric contraction, the muscle shortens whereas, in eccentric contraction, the muscle lengthens during the contraction. Eccentric muscle contraction is important as it can prevent rapid changes in length that may damage muscle tissue and absorb shocks.
What is Isometric Contraction?
The word ‘isometric’ implies constant or unchanging muscle length. In isometric contractions, the muscle length remains constant while the tension varies. Here, the tension develops in the muscle, but the muscle does not shorten to move an object. Therefore, in isometric concentration, when no object is moved, the external work done is zero. In this contraction, individual fibers get shorten even though the entire muscle does not change its length, thus isometric exercises help to strengthen the muscles.
Isometric contraction does not involve joint movement so that the patients requiring rehabilitation may perform isometric exercises to avoid painful movements. These exercises are not recommended for patients with high blood pressure as it can cause a dangerous spike in blood pressure. Example of isometric movement involves gripping an object like a bat or racket. Here, the muscles contract to hold and stabilize the object yet there is no changing length of the muscles when holding them.
What is the difference between Isotonic and Isometric Contraction?

• In isotonic contraction, the tension is constant while the length of the muscle varies. In isometric contraction, the muscle length remains constant while the tension varies.
• Isotonic twitch has a shorter latent period, shorter contraction period, and a longer relaxation period. In contrast, isotonic twitch has a longer latent period, longer contraction period, and a shorter relaxation period.
• Temperature rise decreases isometric tension whereas it increases isotonic twitch shortening.
• The releasing heat of isometric contraction is less and, therefore, isometric contraction is more energy efficient, whereas that of isotonic contraction is more and, therefore, is less energy efficient.
• During isometric contraction, no shortening occurs and, therefore, no external work is done, but during isotonic contraction, shortening occurs and external work is done.
• Isotonic contraction occurs in the middle of a contraction while isometric contraction occurs at the beginning and end of all contractions.
• During the muscle contractions, isometric phase increases when load increases whereas isotonic phase decreases when load increases.


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