The current proposal seeks to index the effect of acute aerobic exercise on excitatory and inhibitory balance using magnetic resonance spectroscopy (MRS) in aging and in chronic stroke. There exists replicated evidence that acute bouts of aerobic exercise increase sensorimotor gamma-aminobutyric acid (GABA) within a two-hour period. Our lab has the technical capability to reliably measure GABA between two sessions and we have developed a functional measure of motor learning that alters GABA in older adults called functional MRS (fMRS). Focal increases in SM GABA due to acute exercise offers the opportunity to test the hypothesis that aging related decreases in motor learning may be related to lower levels of SM GABA. That is, GABA levels may need to increase to a specific level before selective release of SM GABA can afford improved long-term potentiation. This can be evaluated using a cross-sectional approach. However, to date, we have not employed an acute exercise model within our lab for functional MRS. This study will evaluate the feasibility of this approach. Further, as the intent of our research program is to translate aging-related findings to stroke motor rehabilitation, we will use this SPiRE to directly study stroke patients with chronic upper extremity impairment. In light of early findings from a current Merit Award, we now seek to pilot MRS measures in SM in chronic stroke survivors to measure changes in GABA after a bout of acute exercise. To achieve these goals, we will enroll 30 participants in cross-section to test if acute aerobic exercise can have immediate modulatory effects on levels of SM GABA as these relate to motor learning. As these aims involve evaluating the feasibility of a new intervention with two populations (aging Veterans and those with chronic stroke), we believe this offers high impact for motor rehabilitation.