Citrulline increased and L-arginine/ADMA decreased after both TTs, suggesting an exercise-induced increase in eNOS activity and NO production, but we did not observe an improved eNOS activation by CF as there were no differences in L-arginine/ADMA (eNOS substrate) and citrulline (byproduct) after CF intake, neither in rest, nor in response to exercise. This evidence concerns the gene NOS3 and cystic fibrosis.