The EDL muscles of 12-month-old mdx3cv mice display better specific tetanic force than that of age-matched mdx4cv mice at high stimulation frequencies. A: Specific twitch force. B: The force-frequency relationship. C: Relative force decline after 10 rounds of eccentric contraction-induced injury. Sample size, n = 4 for BL6, n = 8 for mdx3cv, n = 6 for mdx4cv. Asterisk, values in BL6 are significantly different from those in mdx3cv and mdx4cv mice; dagger, values in mdx3cv are significantly different from those in BL6 and mdx4cv mice.