Fig 1.
Wooden footboards to alter the width of the base of support during the test.
A: Top of the board, which was attached to the foot with Velcro straps. B: Bottom of the board, which could be removed and replaced by a board with a different width. An anti-slip mat was attached at the bottom of the board.
Fig 2.
Sequence of the conditions during the experiment.
Table 1.
Multilevel correlations (r) and p-value of force plate-based outcomes and TAV. Strong correlations are bold. r = correlation coefficient, TAV = trunk angular velocity, TTS = time-to-stability, CoPS = center of pressure speed, FYdev = the mean variation of the vertical component of the ground reaction force.
Fig 3.
Correlation coefficients of multilevel correlations (black and bold) and within participants correlations (each color is one participant).
Horizontal lines represent the interpretation of the correlations (negligible, weak, moderate, strong, very strong). CoPS = center of pressure speed, TAV = trunk angular velocity, FYdev = the mean variation of the vertical component of the ground reaction force, TTS = time-to-stability.
Fig 4.
Typical example of the signals yielding the four outcome measures in the two seconds before and five seconds after a single perturbation.
The FYdev is colored red from the perturbation onset until it first re-enters the threshold and remains within the threshold for at least one second. From that point onward, it is colored black. In this specific case the TAV score was 0.2 rad/s, the CoPS score was 7.1 cm/s, the FYdev score was 1.8 percentage of body weight and the TTS score was 2.3 s. CoPS = center of pressure speed, TAV = trunk angular velocity, FYdev = the mean variation of the vertical component of the ground reaction force, TTS = time-to-stability.
Table 2.
Results of the repeated measures ANOVA, comparing effect of perturbation amplitude and the width of footboards on force plate-based outcomes and TAV.
Significance of the factors of the ANOVA are presented using P-values. Significant P-values are bold. Effect sizes of the factors of the ANOVA are presented using Partial Eta Squared values. Pert = perturbation, BoS = base of support.
Fig 5.
Bar graph with individual datapoints of force plate-based outcomes and TAV.
Each dot represents the average outcome of one participant for the combination of base of support (BoS) width and perturbation amplitude (pert). Perturbations of 2, 3.5 and 5 cm are represented in blue, orange and grey respectively. CoPS = center of pressure speed, TAV = trunk angular velocity, FYdev = the mean variation of the vertical component of the ground reaction force, TTS = time-to-stability.
Fig 6.
Scatterplots of force plate-based outcomes and TAV of a typical participant.
Each dot represents one medial perturbation, resulting in 72 dots per scatterplot. Perturbations of 2, 3.5 and 5 cm are represented in blue, orange and grey respectively. CoPS = center of pressure speed, TAV = trunk angular velocity, FYdev = the mean variation of the vertical component of the ground reaction force, TTS = time-to-stability.