Fig. 2: Grip strength test, force-velocity relation, power output, and myosin heavy chain expression in EDL muscles of WT and CrT^−/y mice.

A Grip strength test was performed on postnatal day (PND) 40 and PND90. For data analysis, two-way ANOVA, post hoc Holm-Sidak. Data from n = 12. B Relation between force (T, mN) and shortening velocity (V, L₀/s) in WT (black symbol) and CrT^−/y (blue symbol) mice. Lines are Hill’s hyperbolic equations fit to the data (same color codes for data). Inset, same relations with force expressed in kPa after correction of the muscle CSA for the myofibrillar density in the muscle (factor α, see Text). C Power-force relations calculated from data (symbols) and their fits (lines) in B. Inset, same relations with force expressed in kPa after correction of CSA for the factor α. D Mechanical parameters during isometric contraction and during isotonic shortening of muscles from WT and CrT^−/y mice. T₀, maximal isometric force; a/T₀^*, is a measure of the curvature of the force–velocity relation; V_max, unloaded shortening velocity; P_max, maximum power output. T₀^* is the intercept of the Hill equation on the force-axis. In panel D, data are presented as mean ± SEM. n = 4. E and F MHC isoform identification of the EDL muscle fibers by SDS-PAGE in the area of migration of the myosin heavy chains (~220 kDa). In (E) are shown the projections of the mass density along the vertical axis of the bands in (F) after horizontal integration. G Fractional expression of the MHC 2X and 2B isoforms for the WT and CrT^−/y muscles. For data analysis, parametric Student t-test (two-tailed, unpaired) was used. *p < 0.05; **p < 0.01; ***p < 0.001. Temperature 23 °C.