The document describes the different shapes that skeletal muscles can take: parallel or fusiform muscles which run parallel and contract over a great distance but lack strength; convergent muscles which maximize force by converging fibers on the insertion; pennate muscles which have many fibers per unit area and are strong but tire quickly, including unipennate, bipennate, and multipennate types; and circular muscles which surround openings and act as sphincters. Examples are provided for each type of muscle shape.
25. Shapes of skeletal muscles:
1. Parallel or fusiform: as their name implies their fibers run parallel to each other. These muscles contract over a
great distance and usually have good endurance but are not very strong. Examples: Sartorius muscle and rectus
abdominus muscle.
2. Convergent: the muscle fibers converge on the insertion to maximize the force of muscle contraction. Examples:
Deltoideus muscle and Pectoralis Major muscle.
3. pennate: many fibers per unit area. These types of muscles are strong but they tie or quickly. There are three
types of pennate muscle.
unipennate
bipennate
multipennete
4. Circular: the muscle fibers surrounded opening to act as a sphincter. Examples: Orbicularis oris and Orbicularis
oculi muscles.
5. fusiform: some texts classify parallel muscles that are slightly wider in their middle (spindle shaped) as fusiform.
This term will not be used in this course.
