Contractile measurements of muscle fibers in increasing 3D hydrogel concentrations, measured at day 1 of culture. (A) Quantification of resting sarcomere length of muscle fibers in 3D hydrogel. (B) Quantification of sarcomere shortening of muscle fibers kept in 3D hydrogel. (C) Quantification of the contractile velocity of muscle fibers kept in 3D hydrogel. Data are means ± SEM; large dots represent mean values per mouse, and small dots represent single muscle fibers. Significance was determined using a one-way ANOVA with P < 0.05 considered significant.