1. Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, W342 Nebraska Hall, Lincoln, NE 68588-0526 e-mail:
2. College of Public Health, University of Nebraska Medical Center, 984310 Nebraska Medical Center, Omaha, NE 68198-4310 e-mail:
3. Division of Physical Therapy Education, College of Allied Health Professions, University of Nebraska Medical Center, 984420 Nebraska Medical Center, Omaha, NE 68198-4420 e-mail:
4. Mem. ASME Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, W342 Nebraska Hall, Lincoln, NE 68588-0526 e-mail: