The accelerator-brake (or yin and yang) hypothesis has been put forward to explain on one hand, the restrictive myostatin activity to excessive muscle growth (role of chalone) and on the other hand, lower myostatin expression in response to unfavorable metabolic environment, e.g. metabolic syndrome, inflammatory cytokines or uremia [32, 35, 37–39]. This evidence concerns the gene MSTN and metabolic syndrome.