(A and B) Passive tension in EDL muscle (5th toe muscle) was measured in intact muscle, then again after skinning, and a final time after KCl/KI extraction (extraction insensitive tension). The tension is minimally affected by skinning and tensions before and after skinning largely overlap. The difference between before and after KCl/KI extraction is the extraction-sensitive tension. (A) WT, (B) TtnΔ112-158 muscles (note ~4 fold different vertical scales). Insets of A and B show passive stiffness of intact and skinned muscle (SL range 2.45–2.75 μm). Skinning minimally impacts passive stiffness. (C) Comparison of extraction sensitive muscle tension with the passive tension of mechanically skinned single EDL fibers. The inset shows the average stiffness (SL range 2.45–2.75 μm) for single fibers (left two bars) and whole muscle (right two bars). Results are not significantly different, supporting that the extraction-sensitive tension is titin-based (see text for details). (D) Overlay of WT and TtnΔ112-158 skinned muscle total tension, titin-based tension and ECM-based tension. The inset shows the stiffness (SL 2.45–2.75 μm) for titin and ECM stiffness. Both titin and ECM have increased stiffness in TtnΔ112-158 muscles, but the effect is much larger for titin.