What happens to muscle fibers when they contract?

When muscle fibers contract, they undergo a process known as the sliding filament theory. During contraction, the interaction between actin and myosin filaments within the muscle fiber results in the filaments sliding past one another. This action causes the sarcomeres, which are the functional units of muscle fibers, to shorten. As the sarcomeres contract, the overall length of the muscle fiber decreases, leading to the muscle belly thickening and becoming more robust. This physical change is essential for movement and force generation during activities such as lifting, running, or any form of physical exertion. The shortening and thickening of muscle fibers during contraction directly contribute to the overall muscular function and performance.