Fig. 2: Age-related changes in between-stage synergy similarity.

A Representative examples of preprocessed EMG and joint angular acceleration (JAC) signals from the left lower limb of a single subject, with data of five strides shown in each of four infantile walking stages. B For the same subject in (A), KMSs were extracted from the concatenated EMG and JAC matrices at each stage and aligned across the four stages. CH1 included four KMSs, while each subsequent stage included three. To quantify developmental changes in MS and KS for each infant, Pearson correlations (r) between corresponding KMSs, MSs, or KSs at each stage transition were calculated (values for KMS in gray, KS in red, MS in blue). The ACs of multiple gait cycles for each KMS are displayed on the right of the KMS, with individual cycles in gray and the mean profile in red. C Group means of between-stage synergy similarities (KS, MS, KMS) and the duration (in days) between adjacent stages are presented as bar plots with standard deviations, covering the three stage transitions (CH1–CH2: n = 17, CH2–CH3: n = 18, CH3–CH4: n = 20). Statistically significant differences between conditions are indicated by a red line for p < 0.001 or a blue line for p < 0.05. D To assess whether between-stage synergy changes were associated with longer durations between stages, synergy similarities were regressed on the number of days between two consecutive stages for all subjects. In each subplot, observations are shown as blue circles (n = 47) and the fitted regression curve is shown in red. A significant effect was observed for KMS (p = 0.01, solid line), but not for KS (p = 0.62, dotted line) or MS (p = 0.31, dotted line).