A "spirit of infirmity" is of Satan; it saps the
power out of muscles, nerves and tendons
so that they cannot support the body in its
normal posture.

But when Jesus was in the temple and saw
a woman who was bowed over with a spirit
of infirmity fourteen years; He called her
over and said to her, "Woman, thou art
loosed from thine infirmity. And He laid his
hands on her; and immediately she was
made straight, and glorified God."

This infirmity had to loosed or cast off the
woman's body and we must believe the same.