A developmental process, independent of morphogenetic (shape) change, that is required for a myoblast to attain its fully functional state. A myoblast is a mononucleate cell type that, by fusion with other myoblasts, gives rise to the myotubes that eventually develop into skeletal muscle fibers. [ GOC:mtg_muscle GOC:dph http://purl.obolibrary.org/obo/CL_0000056 ]