Figure 6: Geometric and structural response of a 10-month-old K19-null fiber to tensile loading. (a) 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 aligned Z-lines, but discontinuity between fiber deformation and sarcomere strain. This fiber also displays considerable shear, as seen by the slanting of Z-lines (dark lines). A sample region of the fiber that displays particularly well aligned Z-lines that are experiencing some shear is marked with a white box. The boxed region has been computationally enlarged 2x for clarity. There is no slippage or damage of the fiber at the (b) left edge or (c) right edge, imaged in the vicinity of the knot and pins (starred black regions in the periphery of the image) at a moderate fiber strain of 0.5. This may be concluded from the gradual reduction in of the slant of Z-disks away from the knot, which is located to the left in (b) and to the right in (c). Bar = 50 μm.