Proprioception is one of the main standard senses of the body, and arguably one of the most important. Unlike sight, sound, touch, taste, smell and balance, proprioception is an unconscious sense. That is to say it is one we are feeling all the time, and rarely if ever creeps into the conscious mind unless we actually sit down and think about it.
It is the sense of the relative position of neighbouring parts of the body. Every joint, every muscle feeds back into proprioception, helping us know at all times, in the subconscious back of the mind, where our body is, which way it is orientated, and how it is shaped.
This vital sense forms much of our internal awareness. The other senses deal with the outside world only, but proprioception is intimately linked to our sense of self.
Therefore, if we are to pursue the concept of integrating the mind more fully into a virtual form, whether for greater productivity, or to overcome issues arising from a defective physical form, proprioception must feature highly on our list of senses to integrate.
The sense is formed from nerve endings in muscles, in tendons, in organs, and in the skin itself, transmitting back bodily position. Much seems to travel down the vagus nerve, to and from the brain.
The remainder of proprioception is closely linked to pressure sensing (haptic sense, part of touch). It may well be that when we are capable of replicating haptics on a full-body scale, we will replicate most of proprioception as a side effect.
Proprioception is sometimes also called kinesthesia.
Paper: Proprioception: how and why?
Training for Proprioception & Function