Long-term (chronic) muscle stiffness can occur in multiple sclerosis and in conditions where there has been damage to nerves that supply muscles. In these conditions, the muscles shorten (contract) tightly, and can then become stiff and harder to use. This is called muscle spasticity.
This is a companion discussion topic for the original article at https://patient.info/medicine/baclofen-for-chronic-muscle-spasm-lyflex-lioresal