You may describe a skinny person as Heís all skin and bones.
A person who is very thin is a skin and bones.
A thin & srawny person suffering from anorexia nervosa is an anorexic.
An overweight person may be called a fatso or fatty. Itís an offensive Slang.
A muscleman or muscle man (or woman) may be a person "who is physically powerful, especially one with well-developed muscles".
Others might wish to share some other terms with you?