(A) Quantification of the cross-sectional area of muscle fibers in the extensor digitorum longus and soleus muscle of 90-d-old mice and control mice. Individual data points represent mean ± SEM (n = 8); P-value was determined by t test (***P < 0.001, ****P < 0.0001). (B) qPCR analysis showing the levels of MchI, MhcIIa, MhcIIb, and MhcIIx transcripts in the extensor digitorum longus muscle of 90-d-old control or Sam68−/− mice normalized for the levels of the housekeeping gene 18s (n = 3; mean ± SEM); P-value was determined by t test (*P < 0.05). (C) qPCR analysis showing the levels of MchI, MhcIIa, MhcIIb, and MhcIIx transcripts in the soleus muscle of 90-d-old control or Sam68−/− mice normalized for the levels of the housekeeping gene 18s (n = 3; mean ± SEM); P-value was determined by t test (*P < 0.05).