Why can the contraction of muscle tissue cause your arm to bend but a single cell would have no effect?

Muscle tissue is composed of specialized cells called muscle fibers. Each muscle fiber contains numerous myofilaments, which are the contractile elements of the muscle. When a muscle contracts, the myofilaments slide past each other, causing the muscle to shorten and thicken.

The reason why a single muscle cell would not be able to cause your arm to bend is because of the sheer number of cells that are involved in the process. When you bend your arm, you are contracting millions of muscle cells simultaneously. By pulling together in large numbers, the fibers have an impact beyond single-cell activity. Each individual force generated may be tiny from a single contraction of just one cell, but it's combined with the effort of a vast majority to create a discernible motion, like bending your arm.