Of the ~700,000 persons who suffer a stroke each year, only 50% recover the ability to perform unlimited community walking. One mechanism contributing to locomotor dysfunction post-stroke is an increased metabolic cost of walking relative to neurologically healthy individuals 2-4. This increased cost likely limits the amount of walking performed, which further reduces functional capacity, thus contributing to long-term spiral of disability and decreased quality of life in these persons. In addition to increased metabolic cost, increased estimates of mechanical work are also characteristic of hemiparetic walking 2,29. Interestingly, although estimates of mechanical work reflect work done by locomotor muscles, little is known about the impact that peripheral muscle properties have on estimates of mechanical work. Furthermore, questions concerning how these properties relate to the increased metabolic cost of walking remain unanswered. The short-term objective and purpose of the proposed research is to determine the extent to which peripheral muscle characteristics, as well as estimates of muscle mechanical energy expenditure (MMEE), relate to the metabolic cost of walking post-stroke.