Figure 1.
Representation of the measured elevation angles.
Schematic presentation of the elevation angle i.e. the angle between the limb segment and the vertical (A), and an example of the time-courses of the elevation angle for the five segments on one side of the body (B). Note that all elevation angles have been measured for both sides of the body in all participants. The timing (T, horizontal double-headed arrow) of the first peak or valley (P, asterisk; depending on the segment studied), the amplitude (AM, vertical double-headed arrow), and mean (M, dashed line) of the overall trace were determined in all segments (represented here for the upper arm segment).
Figure 2.
Example of the time reversal of an elevation angle trace for BW.
The elevation angle trace for an upper arm (A) and an upper leg segment (B) were time-reversed for BW with respect to FW. There is a great similarity between the revBW and FW trace for the upper arm (represented by a high correlation coefficient R = 0.90), but the similarity for the upper leg is even higher (R = 0.98). Note that this time reversal was applied for all segments in all participants for BW. With FW = forward walking elevation angle trace, BW = backward walking elevation angle trace, revBW = time-reversed backward walking elevation angle trace, R = Pearson correlation coefficient, IC = initial contact and FO = foot off.
Figure 3.
Group average of the upper and lower limb elevation angle traces.
Group elevation angle traces (with positive and negative standard deviation) of the children for the upper and lower limb are presented on the dominant (black, Dom) and non-dominant (gray, Non-dom) side during FW (left column) and revBW (right column). With FW = forward walking elevation angle trace, revBW = time-reversed backward walking elevation angle trace, IC = initial contact and FO = foot off.
Figure 4.
Percentage of children with their respective correlation coefficient between FW and revBW elevation angle traces.
A. The percentage of children with their correlation coefficient are presented for the dominant (black, Dom) and non-dominant (gray, Non-dom) side, and for the upper (right column) and lower extremity (left column) segments. The average of results of the adults are presented by the black (dominant side) and gray (non-dominant side) dots underneath the x-axis of each graph. For representation purposes the correlation coefficients have been divided into ten subclasses (from 0 to 1, with steps of 0.1). Correlation coefficients were deemed very high when R>0.80, high when R = 0.60–0.80, medium when R = 0.40–0.60, weak when R = 0.20–0.40 and very weak when R<0.20. Note that most correlation coefficients are depicted on the right of the spectrum (even more for the lower extremity segments than for the upper extremity segments), which means that most children showed elevation angle traces for FW that correlated very well with revBW elevation angle traces. B. The respective correlation coefficient between the elevation angle trace of FW and revBW corresponding to each participant sorted by age for the upper arm. Note that no maturation effect is apparent during the development on the kinematic reversal from FW to BW.
Table 1.
Comparison of elevation angle trace characteristics and interlimb coordination between FW and BW.
Figure 5.
The effect of Age on elevation angle trace characteristics and interlimb coordination measures.
A. The maximal elevation angle amplitude of the foot (Triangle), lower leg (Diamond), and upper leg (Circle) segment (averaged for Direction) decrease with age in children. B. When including the adults in the statistical group, several elevation angle trace characteristics showed a main effect of Age. B – upper graph. The timing of the first peak (or valley) of the elevation angle trace for the upper leg (Circle) and lower leg (Diamond) decreases with age. B – lower graph. The mean of the elevation angle trace for the upper leg (Circle) increases with age while the mean of the elevation angle of the lower leg (Diamond) segment decreased with age. C – upper graph. Additionally, when the adults were included, the coordination between all limb pairs improved with increasing age (arms [grey Circle], legs [+], Dom arm – dom leg [Triangle], Nondom arm – nondom leg [Diamond], Dom arm – nondom leg [square], Nondom arm – dom leg [empty Circle]). C – lower graph. Also, coordinative stability of all limb pairs (except for the legs) improved during aging. Note that the whiskers represent the standard deviation around the mean.