Pennationswinkel

Pennationswinkel (German for "pennation angle") is the angle between the orientation of skeletal muscle fibers and the line of action of the whole muscle or its tendon. It is a key feature of muscle architecture that influences how fibers generate and transmit force to the skeleton.

Muscles are often classified by pennation pattern: fusiform muscles have fibers nearly parallel to the line of action (small pennation angle), unipennate muscles have fibers angled on one side of a single tendon, bipennate muscles have fibers angled on both sides of a central tendon, and multipennate muscles have multiple tendinous intersections. A larger pennation angle allows more fibers to be packed into a given muscle volume, increasing physiological cross-sectional area and potential force production. However, because only the component of fiber force aligned with the tendon contributes to joint torque, effective force transmitted is reduced approximately by the cosine of the pennation angle.

Pennationswinkel is not fixed; it changes with muscle length, contraction level and training-induced hypertrophy. It is commonly measured in vivo using ultrasound, MRI or inferred from anatomical dissection. Consideration of pennation angle is important in biomechanics, muscle modeling, sports science and rehabilitation because it affects force capacity, shortening velocity and the interpretation of muscle function.