First Attempt Sculpting...Lower legs and lower arms are my issues here, any tips?

As you can see, im having some trouble with my first attempt sculpting. I just cant seem to add enough mesh data, or verts, or really anything, to get the legs and arms to actually have depth. I am laying out muscular structures, with a focus on later cleaning these up into the body shape, as can be seen. What are some good tips to fix this?