CRAT and rheumatoid arthritis: Using available RA skeletal muscle tissue from stored vastus lateralis biopsy samples from patients in this study (n = 9 from the larger cohort of 12 RA participants), we found that the activity of the mitochondrial enzyme carnitine acetyltransferase (CrAT) significantly increased following HIIT (pre-HIIT mean = 23.12 μmol/min/g, SD = 8.24; post-HIIT mean = 26.65 μmol/min/g, SD = 8.20, p = 0.04) (Fig. 3B).