Everyone experiences stiff muscles from time to time, whether after a rigorous workout, in cold weather, or after falling asleep in an unusual position. People with cerebral palsy, stroke and multiple sclerosis, however, live with stiff muscles every single day, making everyday tasks such as extending an arm extremely difficult and painful for them. And since there isn’t a foolproof way to objectively rate muscle stiffness, these patients often receive doses of medication that are too low or too high.