Persons with corticospinal, or upper motor neuron dysfunction have increased muscle stiffness from spasticity. Spasticity is established by clinical examination, but there are few reliable objective measures of spasticity. New ultrasound techniques to measure the elastic properties of tissue represent a potential measure of spasticity. The ultrasound measures of tissue elasticity are painless and quick to perform, but their ability to detect changes resulting from spasticity is uncertain. The goal of this pilot study is to see how much ultrasound measures of muscle elasticity differ between patients with spasticity and healthy controls. Secondary objectives are to correlate muscle elasticity measures with a clinical rating scale of spasticity and to assess intra and inter-rater reliability. This is a protocol for primary lateral sclerosis (PLS) patients who are enrolled in another NIH study in which they have been diagnosed with spasticity.