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Although the risk of foot injuries during walking increases with the foot deformity, the dynamic mechanism is not clearly understood. This study aims at the investigation of dynamic change of center of pressure (COP) in different foot types. Contrasted by previous studies, this study analyzed COP in each gait phase, i.e., loading response, mid stance, terminal stance, and pre-swing. A total of 19 young males participated in this study and the resting calcaneal stance position (RCSP) angle was measured for the classification into three foot types. All participants performed level walking with shoes on. COP trajectory was normalized by foot width and length. In the loading response and mid stance phases COP of Pes Cavus located most laterally ($p<0.05$). No difference among foot types existed at terminal stance and pre-swing phases ($p>0.05$). Foot deformity is known to occur due to the abnormality of musculoskeletal system such as lower extremities muscles, bones, and ligaments. Because the role of musculoskeletal system differs between gait phases, this may have caused phase-dependent COP difference among different foot types.

In this paper we introduce two new mechanisms that developed for a passive walking robot. First mechanism is upper body mechanism which develops to reduce waist assist force and body's stabilizer's energy consumption. This mechanism is employed by one servo and four urethane sheets to operate stabilizer function. This mechanism's experiment results show its low energy consumption and the next step of humanoid robot's upper body mechanism. Second mechanism is ankle spring mechanism which designed to reduce impact force upon walking and reduce waist assist force. This mechanism presents some interesting results and makes a different in waist assist energy consumption. Finally we demonstrate experiment results of two mechanisms that show some interesting points.