What do floaty arms feel like?

A yellow sign with the title 'what do floaty arms feel like?' supported by a stainless steel frame that is bolted to a yellow floor mat.

This old trick (discovered in 1915) shows how your brain and muscles constantly respond and adjust to incoming signals.

How it works

Push the back of your hands against two poles and walk out from between the poles. Many people feel as though their arms float upwards, as though they’re levitating.

Things to try or ask around the exhibit

  • When you very gently step away from the poles, what do your arms feel like?
  • Have your arms ever felt strangely lightweight after carrying a heavy box for a long time?

Background

When you push against the poles, your brain sends nerve signals to release calcium ions into your arm's muscle fibres. One set of muscles contract so your arms can push against the poles. The resistance of the poles becomes a constant stimulus (and a constant source of calcium ions), and your brain and muscle fibres adapt to the resistance.

When you step away from the poles, the constant stimulus is removed. Calcium ions left over in your muscles keep causing your muscles to contract, so your arms rise involuntarily. This muscular after-effect (called the Kohnstamm effect) may also be caused by different areas of your brain—particularly your cerebellum—becoming active as the signals from your limbs change or stabilise.

Finding the science in your world

Sometimes when you’ve been carrying a heavy parcel for a long period of time and you put it down, your arms feel strangely lightweight. This is partly because your brain has adjusted your muscles to the stimulus (heavy parcel) and when the stimulus is suddenly removed, your brain needs to readjust your muscles.