Fig. 4.

Spatiotemporal relationship of iDRP to force and ventral root. A, top: linear regression relating DRP area to ipsilateral (green open circles) and contralateral (red filled circles) force area from a single representative animal. The DRP scales with contralateral force but is independent of ipsilateral force. Each point represents a single cycle (n = 72 cycles). DRP area was strongly correlated with contralateral force (R = 0.77; P < 0.0001) but not ipsilateral force (R = 0.04; P = 0.72). Bottom: linear regression for peak values from another representative animal (n = 95 cycles). Again, DRP magnitude scales with contralateral force (R = 0.83, P < 0.0001) but not ipsilateral (R = 0.03; P = 0.79). When no contralateral force occurs (red points on the y-axis), the DRP is small or zero, but the absence of ipsilateral force (green points on the y-axis) does not affect DRP magnitude. B, C: phase relationships of force and ventral root onset relative to DRP onset. 0° represents the DRP onset and the cycle progresses clockwise from 0° (in-phase) to 180° (out-of-phase) to 360°/0°. Northwest points precede DRP onset, northeast points lag. Arrow length represents the concentration (r) about the mean angle (Ø). B, left: contralateral (red filled circles) and ipsilateral (green open circles) force onset relative to DRP onset. Contralateral force consistently precedes DRP onset. Ipsilateral force is typically out-of-phase with the DRP and contralateral force. When interlimb phasing varies, the DRP stays locked with contralateral force independent of ipsilateral force timing. Right: phasing for all animals. Each dot represents mean angle and r value for a single animal. Arrow length indicates the pooled r value and weighted mean angle for all animals. C, left: contralateral L2 ventral root burst onset relative to DRP onset for the same animal in (A). Right: ipsilateral L2 ventral root burst onset relative to DRP onset from another animal.