When a stroke causes spasticity, muscle stiffness usually locks one side of the body into awkward, tight positions. In the arm, this shows up as a tight fist, a bent wrist, or an elbow pulled inward against the chest. In the leg, it causes a stiff knee or a foot pointing down and inward, making it hard to walk without tripping. Over time, these locked muscles lead to painful spasms and stiff, aching joints. Muscle stiffness after a stroke—medically known as spasticity—occurs