| 摘要: | INTRODUCTION Stepping over obstacles is an inevitable part of daily locomotion. Failure to negotiate the obstacle will result in falls and injuries. Knowledge of the control of the movement is useful for the prevention of falls and treatment of relevant diseases. Although there has been a general consensus that human walk with minimum energy expenditure, it was not the control strategy adopted when stepping over obstacles (Chou et al., 1997). There have been attempts towards finding the actual control strategy (McFadyen et al., 1994; Armand, et al., 1998). A safe and successful obstacle-crossing requires minimum stability of the body provided mainly by the stance limb and sufficient foot clearance of the swing limb. The purpose of the present study was to test the hypothesis that the movement of obstacle-crossing involves a trade-off between minimum energy and maximum foot clearance and is a result of the best compromise of these objectives. MATERIALS AND METHODS Twelve normal subjects crossed obstacles with 10%, 20% and 30% of their leg lengths during level walking while the kinematic and kinetic data were collected with a 3D motion analysis system (VICON 370, Oxford Metrics Ltd, U.K.) and two forceplates (AMTI, Newton, MA, USA), respectively. A height-adjustable obstacle was placed between the force plates. A seven-link model of the human body was developed and used to simulate the motion of obstacle-crossing with multiobjective optimal control theory. The formulated multiobjective optimal control problem took the space positions of the swing ankle at n equal-timed instances during crossing as design variables, Xi, i=1,…,n,. With the anthropometric data of the subject and measured joint angles of the stance leg, the kinematics and kinetics of the body were calculated for a given set of Xi with inverse dynamics analysis. The objectives considered were the energy expenditure (F1) calculated as joint moments times the joint angular velocities and the cl? |
