(A) Representative images of gastrocnemius muscle cross sections stained with H&E or trichrome (top rows, scale bars: 50 μm), or immunolabeled with antibodies specific for periostin (scale bars: 50 μm) or dystrophin-glycoprotein elements (lower panel, scale bars: 100 μm). These images were acquired in RGB colors but inverted to black and white for better visualization. The original panel is presented in Supplemental Figures 2 and 3. (B) Percentage of dystrophin-positive fibers; 600–1000 myofibers were counted per sample, with n = 6 analyzed per group. (C) The collagen area of the gastrocnemius muscle was measured using trichrome-stained cross sections. n = 5 samples per group. (D) Gastrocnemius myofiber area and (E) minimal Feret’s diameter. More than 700 myofibers per sample from n = 6 per group were analyzed. The average values are shown on top of the violin bars. The solid line represents the median, while the dashed lines show the quartiles. (F) Periostin area measured from cross-section muscle sections immunolabeled with specific antibodies against periostin. n = 6 samples per group. (G) Periostin abundance level detected from proteomics analysis of gastrocnemius muscles. (H) Abundance levels of different collagens were measured using the proteomics method from gastrocnemius samples. NS, not significant. *P < 0.05, **P < 0.01, ***P < 0.001 versus WT; ^$P < 0.05, ^$$P < 0.01, ^$$$P < 0.001 versus saline group; ^#P < 0.05, ^##P < 0.01, ^###P < 0.001 versus μDys group; ^&&P < 0.01 versus midi-Dys group using 1-way ANOVA followed by Tukey’s post hoc test. Dys⁺: dystrophin-positive. H&E, hematoxylin and eosin; μDys, micro-dystrophin; mDys and midi-Dys, midi-dystrophin; fDys and full-Dys, full-length dystrophin.