FIGURE 2.

Protocol for stiffness measurement during isometric contraction at saturating [Ca²⁺] (A) and at a similar tension in rigor (B). (Upper traces) Sarcomere length change in nm hs⁻¹. (Lower traces) Force. Horizontal lines are zero force. The same train of steps was imposed on the fiber in both activating and rigor solution. Force per CSA is expressed relative to the CSA in relaxing solution (4500 μm²). Fiber segment length, 2.3 mm; segment length under the striation follower, 0.87 mm. For active contraction, average segment sarcomere length, 2.60 μm; test temperature, 13.0°C. For rigor fiber, average segment sarcomere length, 2.50 μm; CSA, 4300 μm²; temperature, 13.0°C.