The capacity for lean growth may be related to muscle fiber type characteristics. Previously, much emphasis has been placed on contractile phenotype and myosin heavy chain isoforms, yet metabolic properties (oxidative versus glycolytic) may play a more intimate role. Muscle oxidative capacity, largely determined by mitochondrial content and functional properties, has immense potential to fuel anabolic processes including protein synthesis. Yet, enhanced oxidative capacity is also associated with increased protein degradation and may restrict hypertrophy. Intriguingly, the relationships between metabolic phenotype, energy status, and protein accretion change during the lifetime of the animal. Thus, the influence of oxidative capacity on the potential for muscle growth likely depends on growth stage, along with input from various signaling pathways. These signaling pathways integrate cues related to energetic and nutritional status, hormones and other factors; this interplay coordinates adaptations in fiber metabolism, structure, and size to optimize function. In particular, AMP-activated protein kinase (AMPK) plays a key role in regulating energy producing and energy consuming pathways to maintain cellular energy homeostasis. Activated AMPK affects acute regulation of enzyme activity, as well as long-term adaptation through changes in gene and protein expression. Specifically, activated AMPK limits protein synthesis, while simultaneously promoting mitochondrial biogenesis and oxidative capacity. Pigs with the Rendement Napole (RN) mutation possesses a single nucleotide polymorphism in the γ3 subunit of AMPK, which results in increased AMPK activity. Therefore, the RN pig is a valuable model for investigating the effect of AMPK, energy status, and muscle metabolic phenotype on efficiency of lean gain during different stages of growth. Ultimately, understanding the relationship between muscle oxidative capacity and protein accretion and defining how this relationship evolves from birth to adult, is important for maximizing quantity and efficiency of meat production.