Which type of muscle activity involves the contraction of a muscle?

Concentric muscle activity is characterized by the contraction of a muscle as it shortens during movement, enabling the muscle to generate force and overcome resistance. This type of muscle activity occurs, for instance, when lifting a weight or performing a bicep curl, where the muscle fibers contract and lead to the muscle shortening as it produces movement.

In contrast, eccentric muscle activity refers to the lengthening of a muscle while it is under tension, which often occurs when lowering a weight. Isometric muscle activity involves muscle contraction without a change in muscle length or joint position, as seen when pushing against an immovable object. Passive muscle activity does not involve contraction at all, occurring when muscles are not actively engaged but may still be influenced by the forces around them.

Understanding concentric muscle activity is critical for orthotic fitters, as it relates directly to analyzing how the body's muscles function during motion and how orthotic devices can assist in optimizing this function.