Figure 3. Spacing changes during the tetanus rise and during unloaded shortening.

Same experiments as Fig. 2. A and B, spacings of M3 and M6 reflections, S_M3 and S_M6, respectively. Thick and thin lines, and filled and open circles according to the description in Fig. 2A. C. fractional change in S_M3 between rest and tetanus plateau. Continuous lines, sigmoid fits to data lying above 0; dashed lines, sigmoid fit to data starting from the lowest value. In the isometric tetanus (thick lines), the half-time for S_M3 is 31.3 ± 1.6 ms for the continuous line and 30.9 ± 1.4 ms for the dashed line. In the tetanus with initial shortening (thin lines), the half-time for S_M3 is 42.2 ± 1.4 ms for the continuous line and 42.2 ± 1.3 ms for the dashed line. The vertical dashed line marks the end of unloaded shortening. D, fractional change in S_M6 between rest and tetanus plateau. Continuous lines, sigmoid fit to data. Vertical dashed line, end of unloaded shortening.