Inclusion Criteria:  Breast cancer (stade I to III) Patient recieving the first administration of epirubicin-cyclophosphamide (group 1) or paclitaxel (group 2) for early breast cancer treatment  Exclusion Criteria:  History of cancer Known chronic pathology Pacemaker Contraindication to the evaluation of the physical condition Contraindication to the local anesthesia for the muscle micro-biopsy Breastfeeding or pregnant woman