Gait analysis is the systematic study of locomotion. It will be performed in NUH, by a certified medical technician or a trained research staff. Subjects will be required to wear shorts and the whole trial process might be video-recorded for future analyzing the quality of subjects' movement (face will not be captured and consent will be obtained in advance). Markers might be worn at various points of reference of the body such as iliac spines of the pelvis, ankle malleolus, and the condyles of the knee. Electromyography (EMG) sensors might be worn at the area of quadriceps femoris,hamstring, gastrocnemius and tibialis anterior muscles for both legs. Gait parameters of temporal and spatial measures and joint kinematics will be recorded while the subject is walking along the walkway with a force platform, according to the instruction of the medical technician or the trained research staff. Each session will last approximate 1 hour including set-up time.