Acrobats maintain their balance by positioning their centre of mass directly over their base of support, i.e. shifting most of their weight over their legs, arms, or whatever part of their body they are using to hold them up. When they are on the ground with their feet side by side, the base of support is wide in the lateral direction but narrow in the sagittal (back-to-front) direction. In the case of highwire-walkers, their feet are parallel with each other, one foot positioned in front of the other while on the wire.