Orthostatic tremor (OT) is a rare neurological movement disorder characterized by rapid muscle contractions at a high frequency (13-18 Hz) in the legs and sometimes the torso when standing.

In fact, the muscle’s activity resembles the sound of a helicopter, a typical sign of Orthostatic Tremor.

People with OT may not see or sense that their legs are having rapid muscle contractions; it may just feel like unsteadiness, or a loss of balance. The tremors typically aren’t painful while they’re happening, but affected individuals may develop leg muscle pain and stiffness over time.

Going from standing to sitting, walking, or leaning against a wall usually stops or greatly reduces the tremors.