Learning anatomy drawing is important. Period. Whatever you plan to draw and however you plan to draw it you need to have an idea of what it actually looks like, practice in realism, before you plan to move on to creative interpretation.
Here are examples of all different kinds of athletic body types to illustrate the importance of knowing what sort of “built” look you will need to go for when drawing and designing a character. Not all fit is the same fit and it is so hard to find adequate variety when looking for references. These were linked by a talented comic artist Nina Matsumoto. Here site can be found herehttp://ninamatsumoto.wordpress.com/
One of my all time favorite anatomy references is this handy dandy little webpage here. More than 750+ male and female photos in sequence? check. Outstanding b/w lighting on all of them? check. All SFW images but enough skin showing where the muscle placement is? check. Contortion, fencing, parkour and other poses included? checkity-check.