The first aim of the thesis was to evaluate the biological properties of 4 peptides (MSPeps) previously selected (by phage display) for their ability to specifically target myotubes (MSPepIC) or a muscle membrane protein (MMP; MSPepG1-G3). MSPeps were coupled with Rhodamine for imaging and tested in vitro in healthy human muscle cells (54-6 myoblasts/myotubes and 16 UBic myotubes), hepatic cells (HepaRG and HepG2 cell line) and renal cells (HEK293 cell line). A significant increase in uptake of each MSPep was observed in differentiated muscle cells when compared to non muscle cells (HepaRG, HepG2 and HEK293), confirming their muscle specificity. We selected MSPepIC and MSPepG3 as the most specific for muscle-targeting. For the second aim, we first improved MMP translocation at the plasma membrane by mimicking physiological processes in vitro. As expected, improving MMP translocation significantly increased MSPepG3 uptake in differentiated C2C12 murine myotubes. MSPepIC uptake was only moderately influenced by the improvement of MMP translocation.  Finally, to establish a proof-of-concept for FSHD, we designed the coupling of MSPepIC and MSPepG3 to Antisense Oligonucleotides (ASO, 2’O-methoxyethyl (MOE) chemistry) targeting the DUX4 3’UTR. These MSPep-ASO conjugates were synthetized with a FAM fluorophore for imaging and were tested in a DUX4-inducible human muscle cell line (LHCN-M2-iDUX4). Promising preliminary results were obtained since we observed a significant decrease in the percentage of DUX4-positive nuclei for MSPepIC and MSPepG3 conjugates.