MYH6 and sarcopenia: Importantly, weakly scattered slow MyHC (MyHC-I) fibers were markedly increased in aged Scgb3a1−/− TA muscle compared with WT mice, which represents a key fiber transition to hybrid type (type II to type II/I) frequently associated with sarcopenia—the age-related loss of muscle mass and function (Supplementary Fig. S11A, white arrowheads) [34–36].