Mechanics of Single Fiber Contraction

I. Contraction refers to the turning on of the cross-bridge cycle. Whether there is an accompanying change in muscle length depends upon the external forces acting on the muscle.

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition



II. Three types of contractions can occur following activation of a muscle fiber: (1) an isometric contraction in which the muscle generates tension but does not change length; (2) an isotonic contraction in which the muscle shortens, moving a load; and (3) a lengthening contraction in which the external load on the muscle causes the muscle to lengthen during the period of contractile activity.

III. Increasing the frequency of action potentials in a muscle fiber increases the mechanical response (tension or shortening), up to the level of maximal tetanic tension.

IV. Maximum isometric tetanic tension is produced at the optimal sarcomere length lo. Stretching a fiber beyond its optimal length or decreasing the fiber length below lo decreases the tension generated.

V. The velocity of muscle-fiber shortening decreases with increases in load. Maximum velocity occurs at zero load.

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Essentials of Human Physiology

Essentials of Human Physiology

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  • mira
    Why does the muscle fibers shortening velocity increase when the load on the muscle decreases?
    7 years ago

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