Need some help with "lithe" bodytypes

[haneru]

http://tinypic.com/5ai0jr

I've been trying to draw a character that I've had in my head, but people have commented that he isn't muscular enough. I'm not really used to drawing "lithe" bodytypes and most muscle images on the 'net are for very beefed up people. I know some of the muscle in his arms is wrong, could someone point out a resource or offer a critique/draw-over?

Thank you very much!

[Elwell]

Here's a quick drawover of his upper arm anatomy. For this body type I'd look for pictures of swimmers or long distance runners, who tend to be very defined without being "pumped up."
http://img.photobucket.com/albums/v480/Elwell/CA%20pics/haneru_p_o.jpg

[haneru]

Thank you so very much Elwell! I have a difficult time with prominent muscle, I'll definantly practice with swimmer's bodies for reference.
http://tinypic.com/5ape2u

This is how it ended up, does anything still look glaringly wrong?