“…Compared to feedback controllers (i.e., PD and proportional-integral-derivative), which are not optimal in the presence of delays, optimal controllers can model the control of human standing ( Kiemel et al, 2002 ; Kuo, 1995 ; Kuo, 2005 ; van der Kooij et al, 1999 ; van der Kooij et al, 2001 ) and theoretically stabilize human standing with large (>500 ms) delays ( Kuo, 1995 ). This ability, however, rapidly declines with increasing center of mass accelerations ( Kuo, 1995 ), including those driven by external disturbances ( Zhou and Wang, 2014 ). Although feedback and optimal controllers assume that the nervous system linearly and continuously modulates the balancing torques to stand ( Fitzpatrick et al, 1996 ; Masani et al, 2006 ; van der Kooij and de Vlugt, 2007 ; Vette et al, 2007 ), intermittent corrective balance actions ( Asai et al, 2009 ; Bottaro et al, 2005 ; Gawthrop et al, 2011 ; Loram et al, 2011 ; Loram et al, 2005 ) may represent a solution when time delays rule out continuous control ( Gawthrop and Wang, 2006 ; Arsan et al, 1999 ).…”