1. Lauflabor Locomotion Laboratory, Centre for Cognitive Science, Technical University of Darmstadt, 64289 Darmstadt, Germany
2. Biomechatronics Laboratory, Department of Mechatronics and Mechanical Systems of the Polytechnic School of the University of São Paulo (USP), São Paulo 05508-030, SP, Brazil
3. Adaptive Robotics Laboratory, Graduate School of Engineering Science, Osaka University, Toyonaka 560-0043, Japan
4. Graduate School of Engineering, Kyoto University, Kyoto 606-8501, Japan