Why does the arm float automatically? What is the principle?

Scientists call this phenomenon "Kongstam phenomenon".

Principle: In the wake-up stage of Konstam phenomenon, when the arm pushes the wall sideways, the cerebral cortex sends out a signal to ask the arm to push sideways to the maximum angle, and the basal ganglia and inferior nucleus mobilize the corresponding muscle groups.

In the relaxation stage, the signal of cerebral cortex gradually disappears, and there is no inhibitory signal from it. The signal mechanism of basal ganglia and inferior nucleus keeps the previous signal state out of the control of the superior, which is gradually attenuated. This involuntary signal (the basal ganglia is out of conscious control) takes some time to cool to zero.

explain

Generally speaking, Konstam phenomenon is very similar to farmland irrigation. If the irrigation valve is cut off at the source, the water flow will not disappear immediately, but will gradually disappear like a neuron without external interference, so Konstam phenomenon is the same principle.

Such as tremor caused by Parkinson's disease or muscle twitching caused by Tourette's syndrome. Similarly, for example, if you walk with a sandbag for dozens of minutes, your muscles will adapt to this feeling, and then you will feel "light" when you take the sandbag off.