Which fibers are primarily responsible for generating skeletal muscle force?

• A. Extrafusal fibers
• B. Intrafusal fibers
• C. Tendon fibers
• D. Endomysial fibers

Answer: (A)

Skeletal muscle force comes from extrafusal fibers, the main contractile elements of a muscle. When these fibers contract, their actin–myosin machinery shortens, pulling on the tendons and generating the force that moves bones. Intrafusal fibers, by contrast, are inside the muscle spindle and mainly sense stretch to help regulate sensitivity and reflexes; they don’t generate the bulk of the muscle’s force. Tendon fibers aren’t contractile elements but connective tissue that transmitting the force to bone, and endomysial fibers are connective tissue around individual muscle fibers that provide support rather than produce force.