You have big potential. You see how shadows are arranged on the body but still have a bit to learn. I have one advice: don't put a big black line after muscles . In this way (instead of giving deeper) you make the picture look more flat.
thata pretty cool you did that with marker?
Yea here is the sketch http://theone1314.deviantart.com/gallery/25075978#/d3dsheg
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