Aim 1: Determine the in-vivo metabolic characteristics of the ankle plantar flexor muscles in persons with chronic post-stroke hemiparesis and neurologically healthy individuals. In-vivo muscle metabolic properties will be assessed via phosphorous magnetic resonance spectroscopy (31P-MRS). Specifically, we will measure the resting phosphorylation potential as well as the in-vivo oxidative capacity of the ankle plantar flexor muscles. We hypothesize that individuals with chronic hemiparesis will exhibit reductions in oxidative capacity as well as an increased resting phosphorylation potential relative to age-, gender-, height- and weight-matched control subjects. We suggest these adaptations, which are characteristic of a less energetically efficient muscle, contribute to an increased metabolic cost beyond that resulting from potential increases in mechanical work performed by locomotor muscles.