Muscle fiber type composition in the longissimus dorsi muscle of NBW and IUGR pigs at 160 days of age. NBW, normal birth weight; IUGR, intrauterine growth retardation; MyHC I, myosin heavy chain isoform I; MyHC IIa, myosin heavy chain isoform IIa; MyHC IIb, myosin heavy chain isoform IIb; MyHC IIx, myosin heavy chain isoform IIx. abDifferent letters show a significant difference between mean values (P<0.05).