Very fun stuff! Looking at Leonardo di Vinci for information and inspiration with drawing anatomy. I will be posting more of these studies in the future.
I've never formally studied anatomy although I am becoming very interested in it. Well Leonardo's drawings spark my interest in it actually. I love the way he renders muscles and creates depth of mass with extreme dark to light.
Tip: To create depth in a subject remember that the deep areas (furthest from the camera) are extremely dark and as you move closer to the camera it begins to fade lighter. A common problem I've seen with many artists is they don't go dark enough in the darkest areas.
Look at the drawings below
I marked the drawing below in varied areas of value with 3 being the darkest and 1 being "close" to the lightest. The lightest values I didn't mark.