The aim of this review is to elucidate the underlying processes that cause muscle contractures arising in connection with brain injury. We have chosen to compare brain lesions that occur early in life in the developing brain, as in cerebral palsy (CP), or brain lesions that occur late in life to the adult brain, as in stroke. It is generally recognized that deterioration of muscle function and motor skills occurs at different rates depending on whether the injury to the brain happens to the developing or the adult brain. We document structural as well as both physiological and functional changes in muscle contractures after brain injuries in both the developing- and the adult brain. Finally, we discuss the implication of these new findings in relation to diagnostics and therapy.