Isometric vs isotonic contraction

The two primary types of muscle contraction are:

Isometric contraction occurs when the muscle develops tension and exerts force on an object, but does not shorten. In other words, it refers to muscle contraction during which the length of the muscle remains constant. For example, supporting an object in a fixed position, such as carrying a book or a backpack, requires isometric contraction. This type of contraction also occurs when attempting to move an object that is too heavy to shift or reposition. In this case, the muscle may exert maximal force against the object; however, because the object does not move, the length of the contracting muscle does not change. Finally, the antigravity muscles of the back and legs perform submaximal isometric contractions while maintaining posture and for body support.

Isotonic contraction occurs when the muscle shortens under a constant load. For example, when an object is lifted, the muscle contracts and becomes shorter although the weight of the object remains constant. In addition to moving external objects, isotonic contractions are performed for movements of the body, such as moving the legs when walking.

Many activities require both types of muscle contraction. An example is running: when one of the legs hits the ground, isometric contraction of the muscles within this limb keep it stiff and help to maintain body support. At the same time, isotonic contractions in the opposite leg move it forward to take the next stride.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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