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Skeletal muscles work in pairs to move the body. When you bend your arm, the biceps muscle contracts while the triceps relaxes. The biceps 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.

This clip could be used as part of body systems topic to illustrate the function of the biceps and triceps.

Students could label a diagram of the biceps/triceps antagonistic pair of muscles. They could also design, make and evaluate a model of the arm and its muscles, using card and rubber bands. What are the strengths and weaknesses of their model? Can they think of any other antagonistic pairs of muscles, experimenting with body movements in the classroom to test their ideas? Another good example is the hamstring/quadriceps pair in the upper leg which bends and straightens the lower leg.