fCO stimulus (elongation) drives flexor or extensor as observed in , the levator or depressor as observed in (Hess, Büschges 1999, see sect 3.3, red or green dashed squares), and the protractor or retractor as observed by Bässler (1986), red or green dots. Below: activation of fCO stimulus (blue). A) state: forward walking. B) state: backward walking. Abscissa: time (s), ordinate (mV). Dashed lines: simulation data for which no biological results are given. Dotted lines: results from . fCOpos (light blue line) indicates fCO apodeme position, Gamma flexion shows direction of movement. fCO: input to unit swing or unit stance.