Primary outcome measures
Mean WBR. Electronic equipment was used for measuring static standing posture with two force plates (BP400600; Advanced Mechanical Technology, Inc., Watertown, MA, USA). The sampling frequency was set at 1,000 Hz. Thereafter, data was extracted by re-sampling at 100 Hz. Static standing posture was measured for 5 s using two force plates. From the measured data, we calculated the mean WBR using the analysis software (Vicon Nexus 2.12; Vicon Motion Systems, London, UK). Measurements were taken twice, and the second value was used for analysis. The instructions for quantifying posture were to (1) place the feet shoulder-width apart, (2) position the upper limbs at an angle of approximately 30° to the truck, and (3) take measurements for 5 s after confirming that the static standing posture is stable.