Figure 9. Temperature dependence of the various tension components.

The viscosity coefficient obtained from analyses of P₁ tension (A), the relaxation time of P₂ tension analyses (B) and plateau P₂ tension (C) (expressed as a Young's modulus) are plotted against temperature (note that the vertical axes are logarithmic); the lines are fitted regressions to the pooled data but the symbols denote the mean and the vertical bars the s.e.m. Circles are data from fast-twitch fibres; triangles, data from slow-twitch fibres; open symbols at sarcomere length of 2.7 μm; and filled symbols at 3.0 μm. The dotted line in A represents the change in the viscosity of pure water at atmospheric pressure multiplied by 10⁵ (data are from Felix, 1972). Note that all the lines in A have approximately the same slope, suggesting similar temperature dependence, Q₁₀ of ∼1.3: the relaxation time of the viscoelasticity (P₂) has a higher Q₁₀ of 2.4 in the fast-twitch muscle fibres and of 2.0 in the slow-twitch muscle fibres. P₂ tension has an intermediate Q₁₀ of 1.5–1.7 in the two fibre types. In fast-twitch muscle fibres, the plateau P₂ tension at 35 °C could not be accurately estimated by curve fitting (see text): the symbols denote values obtained from the average measurements at three stretch speeds within the plateau region and these were not used in the calculation of the Q₁₀ given above.