spasticity, a neurological problem secondary to an upper motor neuron lesion, has a significant effect on skeletal muscle. the upper motor neuron lesions may be secondary to a cerebral vascular accident, head injury, spinal cord injury, or degenerative diseases such as multiple sclerosis, or perinatal brain injuries such as cerebral palsy. functional ability in these patients can be severely compromised but the basic mechanisms underlying these deficits are not clearly understood. in this review we evaluate the current evidence in the literature that suggests that skeletal muscle tissue itself is altered in spastic conditions. experimental studies were evaluated that included a variety of methods encompassing joint mechanics, tissue mechanics, and muscle morphology. taken together, the literature strongly supports the assertion that ‘spastic muscles’ are altered in a way that is unique among muscle plasticity models and inconsistent with simple transformation due to chronic stimulation or disuse. further studies are required to detail the intra- and extracellular modifications of skeletal muscle that occur secondary to spasticity so that novel therapeutic treatments can be developed for this impairment.