PMC

α increased with the angle of descent for upstroke (F_1,30 = 55.7, η² = 0.458, p = 2.55e-08) and downstroke (F_1,27 = 8.17, η² = 0.122, p = 8.11e-03). However, a significant crossed interaction between species and angle of descent for downstroke chord angle (F_3,27 = 7.68, η² = 0.343, p = 7.26e-4), indicates that the main effect of angle of descent on chord angle during downstroke is uninterpretable (i.e. the response depends on the species). Jitter was added to the points representing horizontal aquatic flights (descent angle = 0) to make all points visible.
Figure 6—source data 1.Chord angle versus descent angle for aquatic flights of four species of alcids.

Diagram of the lateral radiographic images of a participant, which illustrates that the calcaneal-fifth metatarsal angle (CA–MT5 angle) α, also called the arch angle, is defined by lines at the calcaneus and fifth metatarsal. In Taiwan, the criteria for new military conscripts include that individuals are required to serve mandatory service if they have an arch angle <165°, substitute service if they have an angle between 165° to 168°, and are exempt from military service if their arch angle >168°.

Mean change in angle error results when femoral anteversion (FA) angle assumptions are changed in the model. Original mean results (⋅), change in mean results when FA angle is decreased by 10° (x), and change in mean results when FA angle is increased by 10° (*). Dashed lines indicate no angle measurement error (horizontal) and no positioning error (vertical). Sensitivity to FA angle assumption when in flexion/extension for (a) Hilgenreiner epiphyseal angle (HEA), (b) head-shaft angle (HSA) and (c) neck-shaft angle (NSA). Sensitivity to FA angle assumption when in internal/external rotation for (d) HEA, (e) NSA, and (f) HSA.

(A) Estimated polar errors for orientation with various combinations of the azimuth angle and polar angle at S/N = 10. (B) The cross section along the black line in (A) shows the polar angle errors with various polar angles and a fixed azimuth angle of 90°. (C) The cross section along the red line in (A) represents the polar angle errors with various azimuth angles and a fixed polar angle of 60°. (D) Estimated azimuth errors for orientation with various combinations of the azimuth angle and polar angle at S/N = 10. (E) The cross section along the black line in (D) shows the azimuth angle errors with various polar angles and a fixed azimuth angle of 90°. (F) The cross section along the red line in (D) represents the azimuth angle errors with various azimuth angles and a fixed polar angle of 60°.