Fig. 3. Biphasic force-velocity relationship. Force-velocity data collected from a mouse isolated muscle fiber are illustrated in a conventional diagram in (A) and as a semilogarithmic plot in (B). Data in A fitted by Eqn 1 (see Materials and methods) using the following numerical values for constants: k₁=24.08 ; k₂=0.85; a/P₀^*=0.27. Dashed line in A indicates a continuation of the hyperbola derived at low and intermediate loads. The straight lines in B are linear regressions of shortening velocity upon force on either side of the breakpoint of the force-velocity relationship. Note the distinct breakpoint of the force-velocity relationship near 0.8 P₀. Temperature, 23.5°C.