Below the threshold of conscious movement awareness

Means that a physical movement, or the brain's preparation for a movement, occurs entirely outside of your conscious perception and intentional control. 

]In neuroscience and psychology, this concept breaks down into a few clear ideas:

• The Threshold of Consciousness: This is the dividing line where a mental or physical process becomes strong enough for you to notice and report it. If activity stays below this line, you do not feel or know it is happening. 
• Non-Conscious Motor Preparation: Your brain constantly plans, adjusts, and coordinates tiny muscular shifts, balance corrections, and micro-movements automatically. 
• Action Before Awareness: Classic and modern experiments in neuroscience (such as studies on the readiness potential or Bereitschaftspotential) show that the brain's motor cortex often starts setting up a physical movement milliseconds—or even seconds—before you consciously feel the intention to move. 

In short, your nervous system is executing or preparing an action below the "radar" of your waking mind, meaning the movement happens before (or completely without) you ever consciously deciding or realizing you are doing it.