Since exercise training-related changes in RA CD4 + T cell respiration were strongly associated with changes in skeletal muscle fat metabolism pathways (i.e., muscle CrAT enzyme activity and muscle medium chain acylcarnitine concentrations), we hypothesized that RA T cell respiration would also link to the skeletal muscle oxidative metabolism molecular profile and enlighten potential causal pathways. The gene discussed is CD4; the disease is rheumatoid arthritis.