=.2in
Note that unlike variability measures, temporal structure measures are sensitive to the order of the data points in the time series.
Table 2: Stride Time Variability | ||||
3 & 4 Year Olds | 6 & 7 Year Olds | 11--14 Year Olds | ||
SD (msec) | Original Time Series | 55 5 | 31 2 | 23 1 |
After Detrending | 48 4 | 28 1 | 22 1, | |
1st 30 Strides | 47 5 | 25 1 | 17 1, | |
CV (%) | Original Time Series | 6.1 0.5 | 3.3 0.2 | 2.1 0.1 |
Lowest 30 stride segment | 3.1 0.2 | 1.8 0.1 | 1.2 0.1 | |
1st 30 Strides | 5.1 0.5 | 2.6 0.1 | 1.6 0.1 |
SD: standard deviation; CV: coefficient of variation. and denote p < .005 and p < .0001, respectively, compared to the 6 and 7 year olds. denotes p < .0001 comparing the oldest and youngest groups. Kruskal-Wallis tests detected significant differences among the three groups for all measures (p < .0001).
Table 3: Spectral Analysis | |||
3 & 4 Year Olds | 6 & 7 Year Olds | 11--14 Year Olds | |
% High Frequency Power (0.25--0.5 stride) | 0.054 0.010 | 0.064 0.012 | 0.100 0.022 |
Low/High Ratio | 6.8 1.2 | 4.1 0.5 | 2.3 0.5 |
Low/High Ratio after Detrending | 0.30 0.02 | 0.20 0.03 | 0.15 0.03 |
% High Frequency Power (0.3--0.4 stride) | 0.022 0.005 | 0.023 0.004 | 0.038 0.009 |
Low/High Ratio | 6.8 1.1 | 4.5 0.7 | 2.3 0.3 |
Low/High Ratio after Detrending | 0.41 0.06 | 0.29 0.04 | 0.18 0.02 |
denotes p < .05 compared to the 6 and 7 year olds. denotes p < .005 comparing the oldest and youngest groups. Kruskal-Wallis tests detected significant differences among the three groups for all measures except high frequency power.
Table 4: Effects of Age on Stride Time Dynamics | |||
3 & 4 Year Olds | 6 & 7 Year Olds | 11--14 Year Olds | |
Variability | -- | ||
Low/High Frequency Power | -- | ||
Autocorrelation Decay Time | -- | -- | |
Fractal Scaling Exponent | -- |
Compared to the oldest children in whom stride time dynamics are the most adult-like. Note how different aspects of the temporal structure of the stride dynamics tend to mature at different ages. (The low/high ratio was not statistically different in the two youngest groups, however, this representation reflects the observed trend toward a decreased ratio in the 6 and 7 years olds compared to the 3 and 4 year olds.)