1. a Department of Physical Therapy , Khon Kaen University , Khon Kaen , Thailand
2. b Back, Neck and Other Joint Pain Research Group , Khon Kaen University , Khon Kaen , Thailand
3. c Edward P. Fitts Department of Industrial & Systems Engineering , North Carolina State University , NC , USA
4. d Department of Physiology, Faculty of Medicine , Khon Kaen University , Khon Kaen , Thailand