Methods of pre-treating healthy donor's myoblast cultures with growth or trophic factors on transplantation into subjects suffering from myopathic conditions such as muscular dystrophy. Compositions comprising myoblasts and fusion-promoting metalloproteases can be transplanted. Alternatively, myoblasts can be transplanted along with an agent inducing the expression of a fusion-promoting metalloprotease, or a composition comprising genetically-modified myoblasts capable of expressing a fusion-promoting metalloprotease can be transplanted.