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Types of Contraction

المؤلف:  Kim E. Barrett, Susan M. Barman, Heddwen L. Brooks, Jason X.-J. Yuan

المصدر:  Ganongs Review of Medical Physiology

الجزء والصفحة:  25th E, P105

2026-09-05

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Muscular contraction involves shortening of the contractile elements, but because muscles have elastic and viscous elements in series with the contractile mechanism, it is possible for contraction to occur without an appreciable decrease in the length of the whole muscle (Figure 1). Such a contraction is called isometric (“same measure” or length). Contraction against a constant load with a decrease in muscle length is isotonic (“same tension”). Note that because work is the product of force times distance, isotonic contractions do work, whereas isometric contractions do not. In other situations, muscle can do negative work while lengthening against a constant weight.

Fig1. Isotonic and isometric contractions. A) Muscle preparation arranged for recording isotonic contractions. B) Preparation arranged for recording isometric contractions. In A, the muscle is fastened to a writing lever that swings on a pivot. In B, it is attached to an electronic transducer that measures the force generated without permitting the muscle to shorten.