Fig. 3: Distortion of sarcomeric and myofibrillar structures in single EDL muscle fibers from both wt and mdx mice during active Ca²⁺-induced isometric force generation.

a representative example SHG images of a single EDL fiber from a wt mouse (17 weeks) and an mdx mouse (27 weeks) in the relaxed pCa 9 and pCa 6.03 activated states. During mechanical activation, although isometric, the sarcomere lengths visibly shorten and fiber diameters increase. b analysis of the reduction in single fiber sarcomere length during Ca²⁺-dependent force generation (logarithmic plot of specific force) in wt mice (filled circles) and mdx mice (open squares); pCa values color-coded. c, d, changes in myofibrillar/sarcomeric ultrastructural parameters of the cosine angle sum, CAS (c), and vernier density, VD (d), indicate a Ca²⁺-graded increase in the myofibrillar disorder (CAS↓, VD↑) that is more pronounced in the ordered wt EDL fibers, while single fibers from mdx mice are already highly disordered under relaxed conditions