(a) Mesothoracic pro- and retractor activity (2nd and 3rd row, resp.) before and during a front leg inside walking sequence (front leg [FL] stance begin marked in top row event channel), and simultaneous application of load stimuli to the mesothoracic leg stump (bottom trace). Four example responses (grey shaded areas) with expanded time resolution are shown below, the first one during quiescence, the other three during inside steps of the ipsilateral FL. (bi–iii) PSTHs showing the forms of mesothoracic retractor MN response to local load stimuli during FL inside stepping: bi, peristimulus time histogram (PSTH) of retractor activity timed to the begin of the CS stimulus ramp in the quiescent animal. bii, retractor activation upon load stimulus; biii, termination of retractor activity (activation of protractor activity is not shown as PSTH). (c) Distribution of response strength of retractor MNs to CS stimuli throughout the FL step cycle during inside steps with retractor activation from the animal shown in a; note that there is no phase preference for either an increase or a decrease in retractor activation compared to controls, this was also found for all other animals (Figure 3—figure supplement 1). (d) Example for no response to a loading stimulus. (e) Phase plot showing the distribution of CS stimuli in the FL step cycle that lead to protractor activation from N=7 animals; no significant phase preference was detectable. (f) Phase plot showing the distribution of CS stimuli in the FL step cycle that did cause neither re- nor protractor activation from N=10 animals; a significant phase preference was detectable at 0.89. FL: front leg, ML: middle leg, pro: protractor, ret: retractor.