The 3-axis micro-electromechanical system acceleration sensor (LSM303DLM, STMicroelectronics) was surface-mounted on a printed circuit board (17.8 mm × 13.0 mm), which was inserted in a sole, below the arch of foot. The sensor was connected to a commercial micro-control unit (MCU) board (MSP-EXP430G2 LaunchPad, Texas Instruments) with wires. The MCU board provided the sensor with power and inter-integrated circuit communication. The MCU read the acceleration data and sent it to a mobile phone via Bluetooth module (Parani ESD200, Sena Technology, Korea) at 100 Hz. The saved data was analyzed with MATLAB 7.12 (Mathworks) on a PC later.