Simple Biomechanics Experiments

For Young Learners

What This Is

Biomechanics is the study of how forces move a body. The knee is the easiest joint to investigate without equipment, because almost everything it does is visible from the outside.

The six experiments below are observation and measurement. None of them involves loading a joint heavily, testing how far something will stretch, or trying any movement that hurts. That is a deliberate limit and the reason the list is short.

Reading that the knee is a hinge that also rotates is one thing. Watching your own knee rotate while you measure it is another, and the second one stays learned.

These experiments also produce real data for a project, which makes them more useful than a demonstration.

How It Works

1. The screw home movement. Sit with your knee bent, then straighten it slowly while watching the front of your shin. The shin rotates outwards slightly in the last part of straightening. Mark the shin with a sticker and film it to see it clearly.

2. Range of movement. With a protractor or a phone angle application, measure how far your knee bends and straightens. Measure the same knee five times and look at how much your readings vary. That variation is the measurement error every study has to deal with.

3. Standing up without using your hands. Stand from a chair with your arms folded, then again with your feet further forward. It becomes much harder, because the force the knee has to produce depends on where the weight sits relative to the joint.

4. The patella as a pulley. Feel your kneecap with your leg straight and relaxed, then with the muscle tightened. It locks into its groove. The kneecap holds the tendon away from the joint, which increases the mechanical advantage the muscle has.

5. Single leg balance. Stand on one leg with your eyes open, then closed. Time both. Balance depends on information from the joint itself, and removing vision shows how much work that information is doing.

6. Landing angle from video. Film a group stepping down from a low step. Measure the knee angle at the moment the foot lands. People land very differently, and the differences are consistent for each person.

How to Prepare

Read these safety limits before starting, and apply them to every experiment on the list.

Stop if anything hurts. Pain is the instruction to stop and does not need interpreting.

Do not do any of these on a knee that is currently injured, swollen or recovering. Use somebody else's.

No step higher than a normal stair for experiment six, and no jumping.

Do these with another person present, not alone, and on a non slip floor.

An adult supervises any version of these done in a classroom or a club.

For measurements on other people you need their consent, and a parent or guardian's consent for anyone under eighteen. Record readings without names attached.

Common Mistakes

Changing the method partway through and keeping the earlier readings.

Measuring once. Three readings tell you something a single reading cannot, which is how reliable your own measuring is.

Interpreting a reading clinically. A knee that bends less far than another knee has not been diagnosed with anything, and these experiments cannot tell you whether a joint is healthy.

Pushing a movement to find the limit. The experiments measure what a joint does comfortably, not what it can be forced to do.

Comparing readings taken by two different people as though they were the same measurement. They are not, and showing that is itself a good project.

Where to Find Out More

Section 3 of this site covers knee biomechanics in full, including the screw home movement and the mechanics of the kneecap.

Section 11 covers movement assessment as it is done in sport.

If any of these experiments produces a question you cannot answer from those sections, it is a good starting point for a project.