Question

intrafusal is to extrafusal as
voluntary is to reflex.
muscle spindle is to skeletal muscle.
dynamic is to static.
voluntary is to ballistic.

Explanation:

Intrafusal muscle fibers are part of muscle spindles and are involved in reflex - related functions. Extra - fusal muscle fibers are the main contractile elements of skeletal muscles and are responsible for voluntary movement. Just as intrafusal fibers are related to the muscle spindle and extra - fusal fibers are related to skeletal muscle as a whole.

Answer:

muscle spindle is to skeletal muscle.