Various muscle groups enable us to move our body into a large variety of different postures. Postures of this type we can call voluntary, because we can choose to hold them.
The voluntary part of our posture is supplied by using muscle groups to position our body and / or limbs into a particular placement in three dimensional space. Freedom of movement allows us to voluntarily put our bodies into a vast number of different postures for whatever task or whim we are trying to achieve. Use of voluntary posture usually takes place within the structural limits set by the tendons and ligaments.