Capacity, will, and intention are related but distinct concepts. Capacity concerns ability to perform an action; will concerns preference or selection among possibilities; intention concerns undertaking an action deliberately.
Someone may be able to walk yet choose to remain seated. Another person's leg may move because of an involuntary spasm. Both cases involve bodily capacities, but their relation to voluntary agency differs.
These distinctions do not establish human creative independence from God. They explain what is relevant to attributing an act to a morally accountable person.