How do fusiform and pennate muscle shapes differ?

Fusiform muscles and pennate muscles differ mainly in their structural characteristics, which directly affect their function. Fusiform muscles are indeed spindle-shaped, characterized by a wider belly that tapers at both ends. This shape allows the muscle fibers to run parallel to the muscle's long axis, facilitating efficient movement through a greater range of motion. In contrast, pennate muscles have a feather-like arrangement, where the muscle fibers are aligned at an angle to the tendon. This structure allows pennate muscles to pack more muscle fibers into a given space, which increases their power output, though at the cost of a reduced range of motion.

Understanding the differences in shape helps explain their functional responsibilities in the body. The unique architectures enable each muscle type to specialize in different ways of generating force and creating movement. Thus, the spindle shape of fusiform muscles and the feather-like structure of pennate muscles define their capabilities, making option C an accurate differentiation between the two muscle shapes.