What happens to muscle fibers during concentric contraction?

During concentric contraction, muscle fibers shorten as they generate force to overcome resistance. This kind of contraction is typically seen when lifting a weight or performing any movement where the muscle's force exceeds the load it is working against.

As the muscle contracts concentrically, the actin and myosin filaments within the muscle fibers slide past each other, leading to a reduction in the overall length of the muscle. This shortening allows for movements such as raising a dumbbell during a bicep curl. The mechanical action of shortening is crucial for producing movement and is essential for exercises that involve lifting or pushing.

The other scenarios do not apply to concentric contractions. Lengthening would occur during eccentric contractions, where the muscle is lengthening while still under tension, while staying the same length is characteristic of isometric contractions. Becoming rigid is not a normal physiological response during these contractions, as muscle fibers need to maintain flexibility to allow for movement.