Contractile measurements of muscle fibers cultured in 2D and 3D, measured at day 10 of culture. (A) Quantification of resting sarcomere length of muscle fibers cultured for 10 days. The dashed line shows resting sarcomere length values of muscle fibers cultured for 7 days presented in Fig. 2. Note that the resting sarcomere continues to decrease in 2D, while it is maintained in 3D (B) Quantification of sarcomere shortening of muscle fibers cultured for 10 days. (C) Quantification of the contractile velocity of muscle fibers cultured for 10 days. Data are means ± SEM; large dots represent mean values per mouse, and small dots represent single muscle fibers. Significance was determined using Student’s t test with P < 0.05 considered as significant with ** = P < 0.01 and **** = P < 0.0001.