(A,B) In 4 month old male mice, there were no significant differences in the amount of absolute whole muscle contractile generating capacity (Po) generated by the soleus (S), plantaris (P), gastrocnemius (G), tibialis anterior (TA) muscles of Mstn +/+ (n=10; black solid), Mstn +/− (n=9; diagonal) and Mstn −/− (n=7; open) mice (mean ± SE). (C,D) Relative muscle contractile generating capacity (Po/mg) of the S, P, G and TA was impaired in male Mstn −/− compared to male Mstn +/+ and Mstn +/− mice (p = 0.0579 for P Po/mg). Male Mstn +/− G Po/mg was significantly reduced compared to Mstn +/+ mice (mean ± SE). (E) Specific tetanic force (Po/CSA) was significantly less in the S of male Mstn −/− mice compared to Mstn +/+ (mean ± SE). (F) There were no specific differences in G Po/CSA or TA Po/CSA between genotypes (mean ± SE). * p < 0.05 compared to Mstn +/+ mice, † p < 0.05 compared to Mstn +/− mice.