Growth kinetics and population doubling time of both MSCs. The value 1 was substituted for the growth area (GA) occupied by a primary mMSC culture, which corresponded to 9.03 cm2, to simplify the calculation. When the second passage took place, the split ratio at passage 1 (1:3) was multiplied by this value, meaning that at the end of passage 1, the cumulative GA was 3 (i.e., 3 times the growth area occupied by the primary culture). At the end of the second passage, the split ratio at passage 2 (1:2) was multiplied by the cumulative GA at passage 1 (3), resulting in a cumulative GA value of 6 at passage 2. This procedure was repeated for each passage, providing a theoretical growth curve that is directly proportional to the cell number. C57Bl/10: normal, male, 6–8 weeks old; mdx: male, 6–8 weeks old (A). A known number of MSC types from different passages were cultured. The total cover area of cells in the flask was determined at different time points to obtain the doubling time. The values are expressed as means ± SD of 3 independent measurements (B).