Figure 1.

Average head motion during locomotion: example subject. (A) Stride-cycle attractor for linear head acceleration during running. Linear acceleration samples over the 6 min. recording period form a 3D point cloud in the space of possible head accelerations. The surface of this cloud is rendered at a density of 20 points per cubic cm/s². Mean acceleration over the stride cycle defines an attractor in this space (red line). (B–E) Stride-cycle attractors for linear (top) and angular (bottom) head motion during running (left), and walking on a field (right) for an example subject. Traces illustrate the x (blue), y (green), and z (red) components of head motion averaged over all strides. Shaded area indicates SD across all strides. Vertical dashed lines are approximate timepoints of heel strike and toe-off, computed as 5% stride-cycle timing before and after point of maximum z-axis acceleration. Note, linear acceleration plotted in the upper panels is only the component of acceleration due to linear head motion, i.e., the total acceleration (as in A) minus the gravitational component. Orientation data from the sensor was used to estimate and then subtract the gravitational component at each time point.