RSV action on MyHC expression, myotubes dimension, nuclei arrangement in hypertrophy (8 h treatment). A) Immunofluorescence analysis shows hypertrophic morphological changes in MyHC-positive neo-formed myotubes after RSV treatment. Scale bar 50 μm. B) Graphical representation of the significant increment in length, diameter and fusion index of RSV-treated myotubes compared to DM. Significance: *p ≤ 0.05; **p ≤ 0.01. C) Myostatin Immunofluorescence images show the nuclei arrangement to form a ring in the central section of myotube, marker of in vitro hypertrophy and maturation, particularly evident in the DAPI nuclei coloration. Scale bar 50 μm. D) p21 Immunofluorescence images and DAPI also confirm the nuclei arrangement in neo-formed myotubes after RSV treatments in respect to DM condition. Scale bar 50 μm.