Quantification of the hydroxyproline content. n = 7, 7, and 7 for 2-, 14-, and 20-mo-old BL10 mice; n = 9, 7, 7, and 7 for 2, 6, 14, and 20-mo-old mdx mice. *Significantly higher than that of BL10 mice. †Significantly higher than that of 2- and 6-mo-old mdx mice. ‡Significantly higher than that of 14-mo-old mdx mice.