Positions of pivot points in quadrupedal locomotion: limbs and trunk global control in four different dog breeds.

Dogs (Canis familiaris) prefer the walk at lower speeds and the more economical trot at speeds ranging from 0.5 Fr up to 3 Fr. Important works were carried out to understand these gaits at the levels of center of mass, joint mechanics, and muscular control. However, less is known about the global control goals for limbs and overall locomotion, and of whether these global control goals are gait or breed specific. For walk and trot, we analyzed dog global dynamics based on motion capture and single leg kinetic data recorded from treadmill locomotion of French Bulldog (N = 4), Whippet (N = 5), Malinois (N = 4) and Beagle (N = 5). Dogs displayed two virtual pivot points (VPP) during walk and trot each. One resembles control of both thoracic (fore) limbs and is roughly located above and caudally to the scapular pivot, while the second is located roughly above and cranially to the hip and mirrors the control of the pelvic (hind-) limbs. The positions of VPPs and the patterns of the legs axial and tangential functions were gait and breed related. However, breed related changes were mainly exposed by the French Bulldog. The position of VPPs relative to the proximal pivots explains the propulsive and breaking forces observed in quadrupedal locomotion and may help to reduce limb work. In combination with former work, from the present study the VPP template emerges as the expression of a simple and general global control rule for both bipeds and quadrupeds.