Describe how skeletal muscle architecture affects force production.

• A. Parallel fibers produce greater force than pennate.
• B. Pennate fibers shorten more quickly to increase range.
• C. Parallel fibers favor shortening and range of motion; pennate pack more fibers for greater force at the expense of shortening.
• D. Pennate fibers produce the same shortening as parallel but with less force.

Answer: (C)

Muscle architecture determines how much force a muscle can generate and how far it can shorten along its tendon. When fibers run parallel to the line of pull, the muscle can shorten a lot, giving greater range of motion and faster shortening, but the cross-sectional area available to generate force is smaller. Pennate fibers angle toward the tendon, allowing many more fibers to be packed into the same muscle volume, which increases the physiological cross-sectional area and the force the muscle can produce. However, the angling reduces shortening along the tendon and lowers shortening velocity, so range of motion and speed are decreased. This explains why pennate muscles are able to generate greater force at the expense of shortening distance, matching the description that parallel fibers favor shortening and range of motion, while pennate fibers pack more fibers for greater force at the expense of shortening.