Figure 3. Planar covariation of limb segment angular motion.

(A) Ensemble-averaged (±SD across strides) limb segment elevation angles plotted vs.normalized gait cycle and three-dimensional gait loops with corresponding interpolation planes on the bottom are shown for one bird (avocet) and one mammal (elephant). For FL, planar covariation was examined using different tri-segmental FL models: FL_upp – ‘scapula–upper arm–lower arm’ and FL_low – 'upper arm–lower arm–hand’. Note roughly similar orientation of the covariation plane between these two models of FL and different orientation compared to the HL model. (B) Planarity index expressed in percent of variance (PV) accounted for by the third principal component (PC) for HL and FL of animals (PV₃ = 0 for ideal planarity). Source files are available in the SourceData3-Figure3.zip file.

Figure 3—figure supplement 1. Direction cosines of the normal to the covariation plane (the dot product of u₃ with the unit vector along each of the three axes: u_3t, u_3s, u_3f for HL and u_3sc, u_3u, u_3l and u_3u, u_3l, u_3h for FL_upp and FL_low, respectively) for all animals.

Source files are available in the SourceData3-Figure 3—figure supplement 1—souce data 1.zip file.

Figure 3—figure supplement 2. Gait loops in birds and mammals.

(A) Bi-dimensional view of gait loops (Figure 3A) for each animal, projected on the covariation plane. Each loop is rotated so that the first and second principal components are aligned with the vertical and horizontal axes of the figure. Paths progress in time in the counter clockwise direction, touchdown and lift-off events (stance phase in black) corresponding to the top and bottom of the loops, respectively. Animal are labeled as in Table 1. For FL, gait loops for the FL_upp and FL_low tri-segmental models are shown. (B) Relative gait loop width estimated as the amplitude (peak-to-peak) of PC₂ relative to PC₁. Note that the FL_low loop is wider than the HL loop for mammals and the HL loop is wider for birds than for mammals. Source files are available in the SourceData3-Figure 3—figure supplement 2—souce data 1.zip file.