Relationship between muscle growth and myosin gene expression in pigs at different growing stageAbstract. Nineteen pigs (Landrace x Duroc) were used, distributed based on their initial PV as light (15.2 kg), medium (18.2 kg) and heavy (21.3 kg), to identify the muscle in which the abundance of mRNA encoding the Type IIB isoform of myosin heavy chain reflects pig muscle growth. In the light and medium, the Semimembranosus (SM) was the heaviest muscle, but in the heavy the Biceps femoralis (BF) was the heaviest (P < 0.01). In light pigs, the higher expression of RNAm IIB was found in BF and SM (P≤0.05), while the lowest values were for GM, LD and SMT in all pigs. In conclusion, BF and SM are the muscles whose growth is best associated with myosin expression.