Human Musculoskeletal Movement Simulator
Pick a joint, activate a muscle, and watch it flex the joint against a load - with live torque, mechanical advantage and a real load-versus-force experiment.
Pick a joint, set the muscle force, its lever arm, and a load, and watch the bone rotate as torques compete: muscle torque versus load torque.
About the Human Musculoskeletal Movement Simulator
Free human musculoskeletal movement simulator. Pick a joint, activate a muscle, and watch it flex the joint against a load - with live torque, mechanical advantage and a real load-versus-force experiment. Drag, change the sliders and see the result live. No sign-up, works on phone and computer. Built for biology, the human musculoskeletal movement simulator runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Pick a joint, activate a muscle, and watch it flex the joint against a load - with live torque, mechanical advantage and a real load-versus-force experiment. Use it to explore biology ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Human Musculoskeletal Movement Simulator
- Use the controls to change Joint, Muscle force, Muscle lever arm (insertion distance), Load, Load lever arm (hand/foot distance). The simulation reacts instantly.
- Pick an option such as Elbow, Knee, Shoulder, Hip to switch modes or load an example.
- Press "Reset to defaults", "Check equilibrium", "Check mechanical advantage", "📄 Lab Report" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Switch between the elbow, knee, shoulder and hip and compare their default lever arms.
- Increase the load lever arm (hold the weight farther from the joint) and watch net torque flip negative.
- Solve the challenge: find the exact load that balances a 300 N muscle force at a 5 cm lever arm.
Key ideas you can learn
- Torque = force × lever arm (the perpendicular distance from the joint to where the force acts).
- A joint moves when the muscle's torque is bigger than the load's torque, and holds still when they are equal.
- Mechanical advantage = muscle lever arm ÷ load lever arm; most human joints have a mechanical advantage below 1, trading force for speed and range of motion.
- The same muscle force produces less torque the closer its insertion point is to the joint.
Where this is used in the real world
Physical therapists and biomechanists use exactly this torque model to explain why holding a weight at arm's length is so much harder than holding it close to the body.
Who is this simulation for?
Biology students and teachers who want to explore living systems, populations and genetics interactively and safely.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
Why can weightlifters lift heavy loads even though their muscle's lever arm is short?
Muscles generate very large forces, and even a small lever arm still produces enough torque - though it means most of the muscle's force is 'wasted' on the joint rather than the load.
What does mechanical advantage less than 1 mean for a joint?
The muscle must pull with more force than the load weighs, but in exchange the hand or foot moves farther and faster than the muscle shortens.
Is the Human Musculoskeletal Movement Simulator free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Human Musculoskeletal Movement Simulator work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.