Fig. 3.

Dependence of instantaneous (phase 1) stiffness on the temperature-induced increase in fiber isometric tension. These data (filled squares) show fiber stiffness (Young's modulus) to be temperature/tension-independent at and above 6 °C. A weighted linear least-squares fit is applied to these data. Constant stiffness indicates thin filament saturation with myosin heads. The outlier at 1 °C (open square) indicates a loss of saturation. Loss of saturation is mirrored in the discontinuity of the L-jump amplitude data of Fig. 2B. Error bars are mean ± SE.