Neuregulins are growth factors that are essential for myogenesis and regulate muscle metabolism. The addition of a recombinant neuregulin-1 isoform, heregulin-beta1(177-244) (Hrg), containing 3 nmol/l of the bioactive epidermal growth factor-like domain, to developing L6E9 myocytes has acute and chronic effects on glucose uptake and enhances myogenesis. Here, we studied the metabolic adaptation of myocytes to chronic treatments with Hrg.