Hidler J, Brennan D, Black I, Nichols D, Brady K, Nef T. ZeroG : Overground gait and balance training system. J Rehabil Res Dev. 2011;48(4):287-98.DOI:10.1682/JRRD.2010.05.0098

Figure 3. Free-body diagram on plate 2 connected to patient. Spring forces (Fs) and friction forces (Ff) resist motion because of rope forces (Fr). +X = along positive x-axis.

.