It's been a while since I posted here...! But anyway, uh...! I did some redlines for you, which I shall show and then explain! Gasp! Oh no!
HydraTamer_redlines3.jpg [ 62.7 KiB | Viewed 567 times ]
I made the neck less curvy, following the rules of cat/dog/whatever anatomy rather than the bird-like anatomy curvier necks seem to follow since that implies power (you did say you wanted a powerful/muscular dragon) whereas a curvy, bird-like neck probably suggests delicacy and grace and things like that...! In dogs and cats and horses and whatever else, the neck doesn't really bulge before it reaches the ribcage, but sort of flows more smoothly from the head to the chest or uh... something. o_O
Anyway, I also put the dragon in a box with a horizontal line through it. This was to show how the knee, elbow, and chest line up and how the length of the legs from elbow/knee to toes are approximately the same length as the torso is tall (at least the tallest portion of it around where the shoulders are), placing the deepest part of the chest approximately half way between the ground and the animal's back...! In many cases anyway. You can get a better, more detailed explanation of this sort of thing from this tutorial
by Cedarseed, if I haven't already linked you to that before. It's been so long, I can't remember what resources I've given out to whom. o_O
To make your dragon look more muscular, adding some width to those front legs to make them a bit *chunkier* will help! Uhhhh... Other than that, it seems like you've positioned the wings well (I only sort of scribbled lightly over that area with red, though you'd only really need to make changes if you wanted to widen the elbow-to-wrist segment of the wing arm to make it a bit more muscular-looking) and the length of the body seems good! So hurrah!
If you wanted to learn more about muscles and where to place them correctly, it seems that this thread
has a number of references in it that could be of use to you, and if you really wanted something you could have handy all the time for referencing muscles, you could look for a book called An Atlas of Animal Anatomy For Artists
. Some of the linked images in that thread are actually pages from that book (the lion chest and head images, for example) and the rest of the book is filled with detailed diagrams like that of musculature, skeletons, even fur direction from different angles of various different animals!
I hope that all helps you out with your drawing (and future ones) though!