Science // The Human Body

How Muscles Move Bones

Understand that muscles work in pairs to move bones: when one muscle contracts (gets shorter and pulls), the opposite muscle relaxes, and that some muscles are voluntary (we choose to use them) while others like the heart are involuntary (they work automatically)

Ages
7 to 9
Type
Concept
Builds on
2 topics
Leads to
0 topics

Quick check

Can the learner bend their arm and explain that one muscle is pulling while the other is relaxing — and that their heart muscle works without them thinking about it?

Ask this to see whether the topic is secure.

Topic // Mastery

What mastery looks like

What a learner can do once this topic is secure.
  • Demonstrate or describe how biceps and triceps work as a pair to bend and straighten the arm
  • Explain the difference between voluntary muscles (we control them) and involuntary muscles (they work automatically)
  • Name the heart and muscles of the digestive system as examples of involuntary muscles

Topic // Map

Where this fits

What to learn first and what this topic opens up, with the reason for each link. Required links come first.
  • RequiredMust come first
  • HelpfulHelps, but not essential

Before this

2 topics
  • Bones & MusclesRequired

    The Human Body // Ages 5 to 7

    Understanding muscle pairs builds on knowing muscles attached to bones allow movement

  • Naming Major BonesHelpful

    The Human Body // Ages 7 to 9

    Muscle pairs contract to move bones; knowing named bones helps understand which muscles act on them

You are here

How Muscles Move Bones

Ages 7 to 9 // Concept

Leads to

0 topics

Nothing in the catalogue builds on this topic yet. Browse The Human Body

Topic // Research-informed

Teaching notes

From the Marble Skill Taxonomy. These notes have not been validated in classrooms, so treat them as a starting point for your own judgement.

The approach

Teach that skeletal muscles can only PULL (they contract, getting shorter and fatter) and never push. Because of this, muscles must work in opposing (antagonistic) pairs to move a bone both ways: at the elbow, the biceps contracts to bend the arm while the triceps relaxes, and the triceps contracts to straighten it while the biceps relaxes. This is felt best on the child's own upper arm. Second idea: some muscles are voluntary (arm, leg — we choose) and some are involuntary (heart, digestive muscles — automatic). The key misconception to fix is 'muscles push things back' — the partner muscle pulls the other way, and a relaxing muscle does nothing active.

Common misconceptions

  • 'Muscles push bones back into place' — muscles only PULL; the opposing muscle pulls the bone the other way.
  • 'A single muscle moves a bone both ways' — missing that opposing pairs are needed because muscles can't push.
  • 'When a muscle relaxes it goes limp/does nothing important' — relaxing is an active part of the pair's teamwork, letting its partner pull.
  • 'All muscles are under our control' — missing involuntary muscles (heart, digestive muscles) that work automatically.
  • 'The heart is not a muscle' — it is an involuntary muscle that never rests.
  • 'Bigger muscle = the one that straightens' or other guesses — rather than reasoning from which muscle is contracting.

Useful representations

  • Elbow antagonistic-pair diagram: biceps and triceps, one contracting while the other relaxes
  • The child's own arm as the manipulative (feel biceps bunch/relax when bending and straightening)
  • 'Muscles pull, can't push' shown by a muscle shortening to move a bone
  • A hinge-joint model with an elastic band on each side (pull one way, then the other)
  • Voluntary vs involuntary sort (arm/leg vs heart/gut) with 'do you choose to move it?'

Teaching practices

  • Teach 'muscles PULL, never push' first, felt on the child's own upper arm (biceps bunches when bending), because everything else follows from it.
  • Demonstrate the antagonistic PAIR at the elbow: biceps contracts + triceps relaxes to bend; triceps contracts + biceps relaxes to straighten — the pair is why both directions are possible.
  • Have children feel BOTH muscles as they move (one hardens/shortens while the other softens), making 'contract' and 'relax' concrete opposites.
  • Introduce voluntary vs involuntary with clear examples (arm/leg = voluntary you control; heart and gut muscles = involuntary, automatic), linking back to circulation and digestion.
  • Use a simple hinge model (two elastic bands on either side of a cardboard joint) so the pull-only, work-in-pairs logic is visible and manipulable.

Activities to try

  1. 1

    Feel the pair on your own arm

    Why it works: A contracting muscle shortens and pulls a bone; it cannot push. To move the bone back the other way, a second muscle on the opposite side must contract and pull — this is the antagonistic pair. 'Contract' and 'relax' are concrete opposites you can feel.

    1. Place your free hand on the front of your upper arm (the biceps), then bend your elbow to raise your forearm — notice the biceps bunch up, getting shorter and harder.
    2. Keeping your hand there, straighten your arm by pressing your palm firmly down on a table top (or pushing against a wall) — feel the biceps soften. (If you just let your forearm lower slowly on its own, gravity does most of the work and the biceps stays partly tight to control the fall, so the change is harder to feel.)
    3. Now feel the back of your upper arm (the triceps) and press down on the table again to straighten the arm: notice that the back (triceps) tightens while the front relaxes. Straightening against a push like this is what makes the triceps work hard enough to feel.
    4. Say out loud each time: 'Which muscle is pulling now, and which has relaxed?'
  2. 2

    Drive the elbow and discover why a pair is needed

    Why it works: Because a muscle can only ever pull, a single muscle can move a bone one way but is powerless to return it — so a second, opposing muscle is required. This is why muscles come in antagonistic pairs at a joint.

    1. Use a model of the elbow (a driveable on-screen rig, or a cardboard hinge with an elastic band fixed on each side) where each side can act like a muscle pulling.
    2. Make the biceps side pull only (on the band model, pull/tighten the biceps-side band to mimic the muscle contracting — shortening and pulling): watch the forearm swing up as it pulls — the arm bends.
    3. Now try to use that SAME side to push the arm back down straight. Observe that it can only pull one way; it cannot push the bone back.
    4. Make the triceps side pull (the other band): the arm straightens because this muscle now pulls the other way.
    5. State the rule: one muscle pulls to bend, the other pulls to straighten, because neither can push.
  3. 3

    Voluntary or involuntary? Sort the muscles

    Why it works: Voluntary muscles are under conscious control; involuntary muscles (the heart, digestive muscles) work automatically without any decision. The heart IS a muscle — an involuntary one that never stops working, all your life.

    1. For each muscle, ask: 'Do I choose to move it, or does it work on its own?'
    2. Sort examples: arm muscles and leg muscles (voluntary — you decide), the heart and the muscles that squeeze food along the digestive system (involuntary — automatic).
    3. Try the test: you can decide to bend your arm — but try to decide to stop your heart from beating. You cannot. That shows it is involuntary.
    4. Name at least one involuntary muscle from memory (heart; digestive/gut muscles) and explain why automatic control is useful (it keeps you alive without you having to think about it).

Science // The Human Body

More in The Human Body

All 25 topics