For a little STEM to our home school day, I showed Travis a demonstration of how muscles work in opposing pairs. This craft was also a great way to upcycle his latest Kiwi Crate box. Here’s Travis flexing his muscles to get started!

To start, we printed out a printable with shapes of the shoulder, upper arm, and forearm. Place the paper shapes on cardboard and use push pins to mark anywhere that circles are shown. Remove the push pins and cut out the cardboard. Widen each push pin hole with a brad.

Use double-sided tape to attach the bicep and tricep muscle shapes to the upper arm. Insert two brads about half way in the two outside holes (these will act more like bobbins; alternatively, you can use real bobbins if you have them). Push a third brad through the middle hole, inserting it fully, and attach to the shoulder piece.

Insert two brads into the outer two holes of the forearm. Cut two pieces of string 18 inches long and knot around these two lowest brads. Add a center brad on the forearm to attach it securely to the middle arm. You now have something roughly like this:

Loop the top string clockwise over the brads that align with the bicep.

Loop the lower string clockwise around the brads that align with the tricep. Pulling the strings can now allow the arm to flex upwards or downwards, depending which you pull.

For added stability, you can zip-tie the whole apparatus to an empty plastic bottle, but we skipped this step and pulled it more like a marionette’s strings. Have fun having your child see which other muscles move in pairs, like bending a wrist up or down, or bending back and forth at the waist.