This study will test a spinal cord reflex called reciprocal inhibition before, during, and after learning a motor skill to see if the reflex becomes stronger by learning the movement. People learn new motor skills throughout their lives. At first, performing a new skilled movement such as riding a bicycle takes effort and is clumsy, but with practice, it becomes relatively automatic. The motor cortex (a part of the brain) is very active when a new skilled movement is learned, but becomes less active when the movement is over-learned. This study will determine whether the spinal cord helps coordinate the pattern of activity between groups of muscles once a motor skill is learned.