Figure 2. Stiffness measurements during isometric contraction.

A, force development in a sarcomere length clamped twitch (1 mm [Ca²⁺]_o, SL 2.19 μm) with a stepwise reduction in length applied at 95% of T _p. Upper trace: force; middle trace: half‐sarcomere length change; lower trace: motor position. B, superimposed records of force responses (upper traces) and half‐sarcomere length changes (middle traces) elicited by length steps of different sizes imposed by the motor (lower traces). C, T ₁ relationships from data in (B): filled symbols, trabecula; open symbols, half‐sarcomere. The lines are linear regression fits to each set of points. The slopes of the two T ₁ relationships are 0.94 ± 0.02 %/L ₀ (continuous line) and 1.59 ± 0.02 %/L ₀ (dashed line). D, T ₁ relationships of the half‐sarcomere at three different [Ca²⁺]_o: 0.5 mm (diamonds), 1 mm (circles) and 2.5 mm (squares). The lines are linear regression fits to the experimental points. Length of the trabecula, 2.97 mm; segment length, 0.98 mm; average segment sarcomere length, 2.20 μm; cross‐sectional area, 7,600 μm²; temperature, 27°C.