This is a good sart, but you have to have a lot of referanc eon "human" anatomy. Print some sheets ou so you can look at it whilst you model withing zbrush.
The muscles groups are very wrong if you look at anatomy table like I am doing now. The actual surface looks to hard, like rock. If you look at a body builder, pectoral muscles for examples. You can see ton layer and the core layer of muscle tissue.
Strongly recomend you scult , many, many anatomy parts of the body. The torso, the arms, the legs, untill you ge a good feeling of the muscle groups and proporions. Draw also, draw a lot of human anaomy and learn the muscle groups. I know your very empted to jump into characters, but you should learn the "Fundementals" like a sculptor would.
Good luck
