Muscle contraction results in muscle fiber becoming _______.

Muscle contraction occurs when the muscle fibers shorten, which is a fundamental mechanism of how muscles operate. When a muscle receives a stimulus from the nervous system, the actin and myosin filaments within the muscle fibers slide past each other, causing the muscle to pull together and contract. This process leads to a decrease in length, allowing the muscle to generate force and movement.

Understanding the mechanics of muscle fibers is crucial, as the shortening of muscle fibers is what enables actions such as lifting, running, and any physical activity requiring muscle use. The other considerations of lengthening, widening, or stiffening do not accurately capture the physiological response of muscle fibers during contraction. Instead, they relate to different processes or conditions of muscle tissue that are not involved in active contraction.