Fig. 3: Fractionation of muscle synergies during motor development. | Nature Communications

Fig. 3: Fractionation of muscle synergies during motor development.

From: Plasticity of muscle synergies through fractionation and merging during development and training of human runners

Fig. 3

a Changes of muscle synergies for running associated with motor development were studied by comparing the Presch and Sedent0 synergies. Shown are the k-means muscle-synergy cluster centroids (blue, Presch, P-1 to 9; pink, Sedent0, S0-1 to 12), matched by maximizing scalar product (SP). After matching, the component values of every muscle of each cluster were compared between the two groups (dark blue and red, p < 0.05; 2-tailed t-test). The subject-specific clusters – those with synergies contributed by <1/3 of the group – were excluded from matching. We note that six cluster pairs (P- and S0-1 to 6) were moderate-to-well matched (SP between centroids = 0.87–0.99). P values for cluster 4: TA, 0.043; HAM, 0.0046; GLUT, 0.016. P values for cluster 5: TA, 0.016; MGN, 0.015. P values for cluster 6: TA, 0.0047; LGN, 0.0001; VM, 0.0056; RF, 0.0072; TFL, 0.012; GLUT, 0.035. Numbers of synergies within the clusters were, from P-1 to 9, n = 10, 4, 7, 8, 10, 10, 5, 1, 3, and from S0-1 to 12, n = 5, 5, 4, 5, 9, 8, 9, 3, 4, 4, 3, 2. b Presch cluster centroids P-4 to 6 could be explained by linearly combining multiple Sedent0 centroids (SP between original and reconstructed vectors = 0.93–0.99). Thus, each Presch synergy here was fractionated to become multiple synergies in Sedent0 (e.g., P-4 was split to S0-4, 7 and 8). Arrows denote the pattern of fractionation (gray, for P-4; red, P-5; green, P-6). c Synergy fractionation patterns were further characterized by comparing the synergy sets of every of the 90 Presch/Sedent0 subject pairs. Shown is a heat map depicting the percentage of all detected fractionation instances that involved any Presch (P-) cluster producing a fractionation that belonged to any Sedent0 (S0-) cluster. Most instances involved P-4 to 6 fractionated into S0-4 to 8. Gray horizontal and vertical lines separate the matched, unmatched, and subject-specific clusters for Presch and Sedent0, respectively, as indicated in a. Source data for all panels are available as a Source Data file.

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