“…Simulations must be compared to observable states of the system to validate the hypothesis advanced (Cordo et al, 2002 ; Stein et al, 2004 ; Lan and He ), or to propose new testable hypotheses (Bullock, 1993 ). Building a multi-scale model of the sensorimotor system from muscles, proprioceptors to skeletal joints, spinal regulating centers, and central control circuits exemplifies part of this endeavor (Cheng et al, 2000 ; Lan et al, 2005 ; Mileusnic et al, 2006 ; Alstermark et al, 2007 ; Song et al, 2008a , b ; Hao et al, 2013 ; He et al, 2013 ). The review article by Loeb and Tsianos outlined the necessary elements and challenges in this approach, which is the first step toward integrating a vast body of experimental data into a general mathematical framework for simulation.…”