1. a Center for Ergonomics, University of Wisconsin-Milwaukee , Milwaukee , WI , 53201 , USA
2. b Department of Family and PreventiveMedicine, Rocky Mountain Center for Occupational & Environmental Health , University of Utah , Salt Lake City , UT , 84108 , USA
3. c Department of Physical Medicine & Rehabilitation , Medical College of Wisconsin , Milwaukee , WI , 53226 , USA
4. d Department of Mathematics & Statistics , American University , Washington , DC , 20016 , USA