Drawing a human body is not that easy of a task.  One would need to pay attention to details along with what muscles and bones exist within areas, no matter how small.  This also means knowing how they move depending on the poses that an artists wants to draw.  Accuracy is highly stressed.  The proportions must be accurate in both body figures and face features.

It is also important to remember that not everyone is built the same way.  People have different body types and sizes along with different muscle builds.  Some are shorter and stockier while others are big muscled and taller.  Like a snowflake, no two human bodies are the exact same.

I tried to put this into the project by using two different models.  One male and one female, both different heights, and both different in body build.