MSTN and sarcopenia: However the hypothesis that increasing MSTN expression significantly contributes to sarcopenia has subsequently been refuted by a larger study comparing young and frail old men that showed no association between serum MSTN levels and knee extensor strength (r2 = 0.0001, p = 0.97) or quadriceps CSA (r2 = 0.0121, p = 0.48; Ratkevicius et al., 2011).