What features of the internal structure provide the functional activity of the muscles?

Muscles are composed of myofibrils, multinucleated fibers capable of contraction due to the mutual sliding of filaments of actin and myosin proteins. According to the degree of activity, the fibers are divided into white, capable of actively and quickly contracting, but quickly getting tired; and red ones that contract slowly but for a long time. Both types of fibers are present in human muscles, but muscle activity will depend on the predominance of red or white fibers.

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