PMC8209291_01
PMC8209291_02
Experimental setup and gait analysis session overview. (A) Marker locations are denoted by gray circles, and EMG electrode locations by black ovals. 5MT, head of fifth metatarsophalangeal joint; LM, lateral malleolus; LE, lateral femur epicondyle; GT, greater trochanter; IL, iliac crest; WRI, ulnar styloid; ELB, lateral humeral epicondyle; GH, glenohumeral joint; C7, seventh cervical vertebra; EAR, ear; FHEAD, forehead; TA, tibialis anterior; GM, gastrocnemius medialis; GL, gastrocnemius lateralis; SOL, soleus; RF, rectus femoris; VM, vastus medialis; VL, vastus lateralis; BF, biceps femoris; TFL, tensor fascia latae; GLM, gluteus maximus; ES, erector spinae at L2 level. (B) Schematic illustration of principal component (PC) analysis of elevation angles of lower limb segments (thigh: alphat, shank: alphas, foot: alphaf), and its corresponding gait loop plotted three-dimensionally in one representative typically developing child (4 years old) during walking. A loop is obtained by plotting the thigh elevation angle vs. shank and foot elevation angles (after mean values subtraction). The shape and orientation of the gait loop reflect the coordination of limb segments as described by PC1 (reflects the largest variance, which corresponds to the length of the gait loop), and PC2 (the second largest variance, which corresponds to the width of the loop), here indicated with black arrows. Percentage of total variation explained by the three PCs (PV1-PV3) are indicated. Note in adult and older children walking, two principal components typically account for ~99% of the total variance (PV3 = 0.9% in the example). (C) Gait analyses over time (corrected age, in months) for P1-P3 showing supported walking (SW: shades of red), first steps (FS: purple), and independent walking (IW: shades of blue). Different color shades from light to dark indicate the change in age and/or independent walking experience. P3 did not start to walk independently. X means the child did not take any steps during that session.
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F1
P3, the sessions covered a period of 24 months and included five SW sessions (Figure 1C). For P1, a significant increase was found from SW session 1 to IW sessions 3 to 5 (Figure 2 and Supplementary Table 1). For P1, a significant decrease was found between SW session 1 and all sessions (Figure 2 and Supplementary Table 1). For P1, a significant decrease was found between SW session 1 and all sessions (Figure 2 and Supplementary Table 1). The planar covariation of the leg elevation angles is directly related to the dimensionality of the original data set, and the method is shown in Figure 1B. For P1, a significant decrease was found between SW session 1 and all sessions, indicating a reduction in the deviation from planarity (Figure 3 and Supplementary Table 1).
Spatiotemporal gait parameters. Velocity, percentage of double support and stance duration from S1 to S5. Error bars indicate SDs. For the percentage of double support and stance duration of P2, the most affected side (dark color) and least affected side (light color) are shown, whereas for P1 and P3, one side is shown. Significant linear differences across sessions are denoted by asterisks, and significant interactions between session and side are denoted by lines between the most and least affected sides for P2 (p < 0.05).
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F2
For P1, a significant increase was found from SW session 1 to IW sessions 3 to 5 (Figure 2 and Supplementary Table 1). For P1, a significant decrease was found between SW session 1 and all sessions (Figure 2 and Supplementary Table 1). For P1, a significant decrease was found between SW session 1 and all sessions (Figure 2 and Supplementary Table 1). IW sessions 3 to 5, and of GLM from FS session 2 to IW sessions 4 to 5. In contrast, FWHM significantly decreased from FS session 2 to IW session 3 for TFL, and to sessions 3 to 4 for VM (Figure 4B and Supplementary Table 2). FWHM of SOL, VM, VL, and ES already increased during FS session 3. In the least affected side of P2, FWHM of GM, VM, BF, and GLM significantly increased during IW sessions 4 to 5 compared to SW session 2, whereas FWHM of RF, TFL, and ES already increased during FS session 3. FWHM of SOL was only significantly larger during IW session 5 compared to SW session 1 (Figure 4B and Supplementary Table 2). FWHM of TA, SOL, VM, BF, and TFL was significantly smaller in session 1 compared to all other sessions. FWHM of GM and GLM was significantly larger during sessions 4 to 5 and of GL during sessions 2, 3, and 5, compared to the first recorded session (Figure 4B and Supplementary Table 2).
Intersegmental coordination. Gait loops plus the corresponding mean percentage of total variance explained by the second and third eigenvectors (PV2 and PV3), and the mean orientations of the normal to the plane (u3t) are shown from S1 to S5 for each participant. Error bars indicate SDs across strides. For P2, the most affected side (dark color) and the least affected sides (light color) are shown, whereas for P1 and P3, one side is shown. Significant differences with session 1 are marked by asterisks, and significant interactions between session and side are denoted by lines between the most and least affected sides for P2 (p < 0.05).
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F3
In summary, Figure 3 shows the mean gait loops for all sessions of each participant and its corresponding values of planar covariation. For P1, a significant decrease was found between SW session 1 and all sessions, indicating a reduction in the deviation from planarity (Figure 3 and Supplementary Table 1).
EMG activity. (A) Muscle activation patterns averaged across strides per session for P1-P3, for the most and least affected legs in P2. The peak around foot strike is emphasized in the zoom-in view of the TA muscle of P3. (B) Full-width of the half maximum (FWHM) per muscle per session in P1-P3. TA, tibialis anterior; GM, gastrocnemius medialis; GL, gastrocnemius lateralis; SOL, soleus; RF, rectus femoris; VM, vastus medialis; VL, vastus lateralis; BF, biceps femoris; TFL, tensor fascia latae; GLM, gluteus maximus; ES, erector spinae at L2 level. *Significant difference compared to the first recorded session of this muscle.  All sessions are significantly different from the first recorded session.
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F4
All activation patterns became smoother and displayed increasingly distinct peaks (Figure 4A). A short burst of activity was present around foot strike in the TA and calf muscles (GM, GL, and SOL) of P3 during all sessions (see zoom-in view of P3 Figure 4A), in the SW and FS sessions of P2, in particular in the most affected leg. IW sessions 3 to 5, and of GLM from FS session 2 to IW sessions 4 to 5. In contrast, FWHM significantly decreased from FS session 2 to IW session 3 for TFL, and to sessions 3 to 4 for VM (Figure 4B and Supplementary Table 2). FWHM of SOL, VM, VL, and ES already increased during FS session 3. In the least affected side of P2, FWHM of GM, VM, BF, and GLM significantly increased during IW sessions 4 to 5 compared to SW session 2, whereas FWHM of RF, TFL, and ES already increased during FS session 3. FWHM of SOL was only significantly larger during IW session 5 compared to SW session 1 (Figure 4B and Supplementary Table 2). FWHM of TA, SOL, VM, BF, and TFL was significantly smaller in session 1 compared to all other sessions. FWHM of GM and GLM was significantly larger during sessions 4 to 5 and of GL during sessions 2, 3, and 5, compared to the first recorded session (Figure 4B and Supplementary Table 2). Supplementary Material 1. Similar to the results shown in Figure 4B, this analysis revealed clear changes between different sessions in P1 and P2.
Muscle synergies. (A) Variability accounted for (VAF) by one to eight synergies, and for the first synergy (VAF1). (B) Synergy activation patterns for a fixed number of synergies: four for P1 and P2, and two for P3. (C) Full-width of the half maximum (FWHM) per muscle synergy. (D) Synergy weights: contribution of each muscle to each synergy across sessions.
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F5
FS to IW. VAF1 was higher for the most compared to the least affected leg during the FS and IW sessions, but vice versa for the SW session. For P3, VAF1 slightly differed between sessions, but there was no clear trend (Figure 5A). Synergies were ordered based on the highest correlations between the synergy weights per session (Figures 5B,C). Despite the development in synergy activation patterns in P1 and P2, the synergy weights appeared similar across sessions (Figure 5D).