“Biqi” Bayberry Extract Promotes Skeletal Muscle Fiber Type Remodeling by Increasing Fast Myofiber Formation via the Akt/FoxO1 Pathway in Mice

Bayberry is known to be a rich source of natural flavonoids and has been reported to have various health-promoting abilities. However, its function on regulating skeletal muscle fiber type remains unclear. This study examined whether bayberry extract affects skeletal muscle fiber type by promoting fast myofiber formation, as well as the potential molecular mechanism. After eight weeks, the “Biqi” bayberry extract (BBE) groups mice displayed markedly enhanced grip strength and improved metabolic rate compared to the control group mice. BBE also significantly increased myofibers size, LDH activity, MyHC-IIb (fast-twitch mRNA) expression, and the percentage of fast-twitch myofibers, while decreasing SDH activity, MyHC-I (slow-twitch mRNA) expression, and slow-twitch myofibers percentage in the skeletal muscle of the mice. The effect of BBE on regulating skeletal muscle fiber type remodeling is likely attributed to its activation of the Akt-FoxO1 pathway. Our findings indicated that BBE can effectively regulate the expression and proportion of fast-twitch fibers, making it a potential therapy for improving glucose homeostasis of skeletal muscle.