CD4 and rheumatoid arthritis: Following HIIT, changes in RA cardiorespiratory fitness were significantly associated with changes in RA peripheral CD4 + T cell basal and maximal respiration (Spearman’s rho = 0.89, p = 0.02 for both; Fig. 1F-G) and OCR/ECAR ratio (rho = 1.00, p < 0.001; Fig. 1H).