Pennate

Pennate is a term used in anatomy to describe a muscle architecture in which muscle fibers are oriented at an angle to a central tendon, giving a feather-like arrangement. The term derives from Latin pennatus, meaning feathered.

In pennate muscles, fibers insert into a central tendon or into septa extending from it. This design increases the muscle's physiological cross-sectional area, allowing greater force production within a given muscle volume, but at the cost of shortening velocity and excursion, reducing range of motion.

Depending on the arrangement, pennate muscles are classified as unipennate (fibers on one side of a central tendon), bipennate (fibers on both sides of a central tendon), or multipennate (multiple tendon rami with interdigitating fibers). The multipennate arrangement is common in muscles that generate high force in a compact volume; unipennate and bipennate arrangements are found across the body.

Pennation angle—the angle between fibers and the line of action—can increase as the muscle shortens, affecting force transmission and shortening velocity. The architecture is a key factor in muscle function, influencing how force is generated and transmitted to tendons.

Overall, pennate architecture emphasizes force over velocity compared with parallel-fiber designs, reflecting a trade-off that suits different functional demands in locomotion and posture.