Spasticity, or greater muscle resistance, is a major disabling condition following stroke. Recovery of lost motor function in patients with stroke may be affected by spasticity, which most commonly develops in elbow and ankle muscles. However, despite its clinical relevance, the natural development of spasticity over the first 3 months after stroke is not clearly understood. Indeed, common clinical measures of spasticity such as the Modified Ashworth Scale (MAS) do not take into account the neurophysiological origin of spasticity and lack reliability and objectivity. The objective of this study is to examine the natural history of the development of spasticity among patients with stroke over the first 3 months using a new neurophysiological measure (TSRT, the tonic stretch reflex threshold angle) and its velocity sensitivity (mu) in comparison to MAS and other common clinical tests. In addition, detailed brain imaging will be used to understand the relationship between damage to brain regions relevant to the development of spasticity and TSRT/mu values. It is hypothesized that 1) TSRT/mu will indicate the presence of spasticity earlier than MAS/clinical tests; 2) TSRT/mu measures will be more closely related to motor impairments and activity limitations than MAS; 3) the lesion severity (identified by imaging) will be related to the change in TSRT/mu values. Outcomes will be measured in a pilot cohort of 12 patients hospitalized for first-ever stroke. Measurements will be taken at the bedside within the 1st week of the patient's admission and will be done once per week for 12 weeks with a follow-up at week 16. Brain Imaging will be done around the 6th week post-stroke.