What better way to learn about muscle than by dissecting one? Using cow muscle (beef), learners compare bundles of yarn to muscle fibers as they explore each. The supplemental reading about astronauts losing muscle mass in space and what types of tests are being conducted to combat that atrophy adds real-world value to the instructional activity, as well as a hook to engage kids. Although the publisher states the instructional activity is for grades 3-12, it is most developmentally appropriate for middle school or high school.