National Institutes of Health
Nih Curriculum Supplement for Middle School: Looking Good, Feeling Good
A great resource from the Office of Science Education which provides a curriculum for teaching about the musculoskeletal system, the skin system and how they interact. This curriculum emphasizes choices teens can make to ensure good...
Biology Pages
Kimball's Biology Pages: Muscles
Everything you've ever needed to know about muscles. To be used as classroom notes or a supplement for learning.