Skeletal muscles work in pairs to move the body. When you move your arm, the bicep contracts while the triceps muscle relaxes. The bicep pulls the bones together, bending the arm. The reverse happens when the arm straightens. Muscles can only contract and pull bones - they never push them.
The movement of muscles and structure of muscle tissue could be looked at in more detail, with students investigating what happens when muscles contract. Students could explore the difference between reflex and voluntary muscle movement and explain the relation of muscles to nervous control.