Some proteins characteristic of fast-twitch fibers (e.g., PVALB, MYH4, MYLPF, and TNNI2) were increased, whereas some proteins characteristic of slow-twitch fibers (e.g., MB, MYL2, MYL3, TPM2, and TNNI) were decreased, suggesting an increase in the ratio of fast/slow-twitch fibers in the gastrocnemius muscles of RA rats. Here, MYH4 is linked to rheumatoid arthritis.