Figure 1.
Schematic representation of the definition of the backward (BW) and medio-lateral (ML) margin of stability (MoS).
A: The ML MoS is defined as the minimum distance in medio-lateral direction between the extrapolated centre of mass (XCoM; dotted line in the right panel) and the lateral border of the foot attained during foot-contact (solid line in the right panel). The XCoM is calculated as the position of the centre of mass (CoM; dashed line in the right panel) plus its velocity (vCoM) times a factor √(l/g), with l being the length of the pendulum (for which often the leg length is used) and g the acceleration of gravity B: The BW MoS is defined as the distance in anterio-posterior direction between the XCoM (dotted line in the right panel) and the posterior border of the leading foot (solid line in the right panel) at initial contact.
Figure 2.
Visual feedback given during the experiment.
Each cell corresponds to a certain combination of stride frequency and stride length. The middle cell corresponds to the combination of comfortable stride length and stride frequency. The percentages of comfortable stride length and stride frequency that correspond to the other cells are given in figure 3. For each experimental trial one of the cells became light gray to represent the required combination of stride length and stride frequency for that specific trial, while the red dot represented the real-time feedback on the combination of stride length and stride frequency that subjects were using.
Figure 3.
Schematic overview of the experimental conditions.
(V: Walking speed; SL: Stride length, SF: Stride frequency). Percentages are percentages of respectively comfortable walking speed, stride length, and stride frequency. The rows represent the stride length manipulations and the columns the stride frequency manipulation. Note that walking speed on the diagonals reached a constant percentage of comfortable waking speed.
Figure 4.
Results for ML MoS, BW MoS, and LDS.
ML MoS (A), BW MoS (B), and λs (C) as a function of both stride length and stride frequency (left column). Light (yellow) areas represent a high value, while a dark (red) areas represent a low value for the concerning outcome measure. In the middle column the figure is oriented such that the relation between stride frequency and the outcome measure stands out. The same is done for stride length in the right column.
Table 1.
GEE regression coefficients (β) for the effect of stride length, stride frequency and walking speed on the one hand and the ML MoS, the BW MoS and LDS expressed as λs on the other hand.