Fig. 6. (A) Maximum tensile (_t, open circles) and compressive (_c, filled circles) stresses acting in the right femur and neutral axis angle from the anatomical AP axis of the femur from an individual cooter. Plots show means (±s.e.m.) over N=20 trials. Frame stills show limb position at the time of maximum tensile stress (left image) and at the time of peak net GRF magnitude (right image). Solid vertical lines mark the relative timing of these loading events. (B) Schematic cross-sections of a right femur illustrating neutral axis orientations for bending (red line and values) at peak tensile stress (upper) and peak net GRF (lower). Neutral axis is illustrated offset from the centroid (dark circle) due to axial compression superimposed on bending loads. Mean rotation of the neutral axis >45° over the course of a walking step indicates that the `posterior' cortex of the femur experiences compression (shaded) and the `anterior' cortex experiences tension (unshaded), placing the plane of bending nearly parallel with the anatomical dorsoventral (DV) axis of the bone. The curved black arrow indicates the inward rotation of the femur during a step, which shifts the anatomical plane of bending to align more closely with the anatomical DV axis.