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Figure 4: Geometric and structural response of a 10-month-old wild-type fiber to tensile loading. The same region of the fiber, imaged using phase-contrast microscopy, is shown at five different deformations. Fiber strains, radial strains, and sarcomere lengths are reported to the right of the fiber for each deformation. The fiber displays well aligned Z-lines (dark vertical stripes), consistently increasing sarcomere strain, and decreasing fiber diameter with increased fiber deformation. A sample region of the fiber that displays particularly well aligned Z-lines that are experiencing some shear, inferred through the slanting of Z-lines, is marked with a white box. The boxed region has been computationally enlarged 2x for clarity. At high strains ( 𝜀 F > 0 . 8 ), artifactual thickening of  Z-lines occurs due to shear-induced offsets of Z-lines in deeper regions of the fiber. Bar = 50 μm.