Fig. 4. Kinematic modulation in relation to muscle activity. (A) Characteristic range of downstroke tip trajectories. Downstroke deviation was defined as the deviation () value at an elevation () of 0 rad (indicated by white circles). Ventral amplitude was defined as the maximum elevation () value during the ventral reversal (indicated by black circles). (B) Downstroke deviation and ventral amplitude of each cycle plotted as a function of time. Downstroke deviation points are color-coded according to the occurrence of a b2 and b1 spike (red), a b1 spike only (green) or the absence of basalare muscle spikes (open circles) within the cycle. Ventral amplitude points are color-coded according to burst activity in III2–4 (blue) or I1 (pink). The blue points were defined as Mode 2 and the pink points were defined as Mode 1. (C) Occurrence of spikes in muscles b2, b1, I1, III1 and III2–4. The blue, horizontal bar indicates maximal activity in III2–4, and the pink, horizontal bar indicates minimal activity in III2–4 paired with I1 activity. Plots in B and C share the same time scale.