Title : Modulation of phase durations , phase variations and temporal coordination of the four 1 limbs during quadrupedal split - belt locomotion in intact adult cats

50 Stepping along curvilinear paths produces speed differences between the inner and outer 51 limb(s). This can be reproduced experimentally by independently controlling left and right speeds with 52 split-belt locomotion. Here, we provide additional details on the pattern of the four limbs during 53 quadrupedal split-belt locomotion in intact cats. Six cats performed tied-belt locomotion (same speed 54 bilaterally) and split-belt locomotion where one side (constant side) stepped at constant treadmill speed 55 while the other side (varying side) stepped at several speeds. Cycle, stance and swing durations 56 changed in parallel in homolateral limbs with shorter and longer stance and swing durations on the fast 57 side, respectively, compared to the slow side. Phase variations were quantified in all four limbs by 58 measuring the slopes of the regressions between stance and cycle durations (rSTA) and between swing 59 and cycle durations (rSW). For a given limb, rSTA and rSW were not significantly different from one 60 another on the constant side whereas on the varying side, rSTA increased relative to tied-belt locomotion 61 while rSW became more negative. Phase variations were similar for homolateral limbs. Increasing left62 right speed differences produced a large increase in homolateral double support on the slow side while 63 triple support periods decreased. Increasing left-right speed differences altered homologous coupling, 64 homolateral coupling on the fast side and coupling between the fast hindlimb and slow forelimb. 65 Results indicate that homolateral limbs share similar control strategies, only certain features of the 66 interlimb pattern adjust and spinal locomotor networks of the left and right sides are organized 67 symmetrically. 68 69