There are over 600 muscles in the human body that we can strengthen, stretch, flex, or simply leave alone. Whether we use them consciously or not, muscles work to protect our bones and keep our blood flowing. In this volume, readers will learn about the different kinds of muscle and why muscles are so essential to everything we do—from eating to smiling to mastering a sport. Labeled diagrams complement text and highlight important muscles in the body, while boxed questions encourage readers to think critically about the information they learn.