Robust Gait Kinematics under Two Different Gravitational and Viscous Conditions in Human

Many neurophysiological and behavioural studies suggested that end-effector trajectory might be centrally represented variable within the gravity reference frame and effectively controlled. To this end we examined the effects of gravitational loading and viscosity upon lower limb kinematics during walking in water (WW) and on land (LW). Seven healthy, young male subjects were asked to walk on a force platform along the walkway. In water-experiment, the depth was adjusted to the level corresponded to about 20% of the body weight. Walking speed was self-determined (comfortable) and faster in water, while that on land was comfortable and slower. Additional load (8 kg) was also applied. The spatio-temporal patterns of the lower limb end-effector, three joint angular displacements (hip, knee, and ankle) were analyzed during the stance phase of each walking condition using a motion analysis system. Paths and curvature profiles, and area of end-effector displacements, range of motion in three joint angular displacements were computed and compared in each walking sessions. Three joint net moments calculated from angular displacement profiles and ground reaction forces were also computed and compared in each walking sessions. The results revealed that the end-effector trajectory, joint angular displacement of hip and ankle showed similar pattern during WW compared with those of LW. In addition, the range of motion at the knee joint was decreased during WW. However, the joint moments in all three joint were decreased and had different functional meanings throughout stance phase. These results suggest that conservation of lower limb kinematic templates across WW and LW does not arise from dynamical constraints but would reflect a behavioral execution achieved by the central networks involved in the control of motion. Moreover, the changes in the joint moments may reflect a differential recruitment pattern of muscles during WW comparing with those of LW.