Breast cancer (BC) is the most common neoplasm in Chile, and its medical treatment leads to high survival. One-third of survivors will develop BC-related lymphedema. Lymphedema is a chronic condition characterized by increased volume in the ipsilateral arm to surgery. A higher volume is associated with decreased physical functionality and quality of life. Recent studies suggest that resistance training could control arm volume through increased muscle mass development, improving physical functionality and quality of life for patients. To our knowledge, there is no study that has analyzed the effect of a resistance training program among women at risk of BC-related lymphedema on arm volume and quality of life. The purpose of this study is to determine the effect of resistance training on the arm volume and quality of life among women with adjuvant chemotherapy and high risk of BC-related lymphedema compared to a control group with regular physical therapy management, which does not include resistance training.

This is a randomized controlled study. It will be held at the Complejo Asistencial Dr. Sotero del Río, which receives all patients from the South East Metropolitan Health Service. Participants: 106 women receiving adjuvant chemotherapy for BC who have undergone axillary lymph node dissection or with obesity will be recruited. The difference in volume between the arms will be evaluated with optoelectric equipment. Quality of life with The European Organization for Research and Treatment in Cancer Quality of Life C-30 (EORTC QLQ-C30) and the European Organization for Research and Treatment of Breast Cancer-Specific Quality of Life Questionnaire BR23 (EORTC QLQ-BR23) questionnaires, both validated in Chile; the handgrip with a dynamometer; and physical functionality with the six-minute walk test. Volunteers will be randomly assigned to the resistance training group or control group. The resistance training group will consist of twice a week supervised sessions, for 12 weeks. The exercises will be for arms and legs, self-loading type, and with external weights. The control group will follow the usual physical therapy management, which does not include resistance training. Subsequently, volunteers will be evaluated at the third and sixth months after completion of the 12 weeks resistance training program.

Inclusion Criteria:

• Newly diagnosed with stage I-III breast cancer, histologically confirmed.
• Patients scheduled to receive adjuvant post-operative chemotherapy.
• Partial or total mastectomy with axillary node dissection.
• Partial or total mastectomy with sentinel node dissection with body mass index between 30.0 and 39.9 kg/m2.
• Approval of their treating physician to participate in sub-maximal physiological fitness testing and a low to moderate progressive resistance exercise program.

Exclusion Criteria:

• Inter-limb volume difference greater than 200 ml or 10%.
• Previous antineoplastic treatment (chemotherapy, radiotherapy, or endocrine therapy).
• Breast cancer stage IV
• Unable to participate in an exercise program related to other medical problems.
• Be identified as vigorous exercise behavior related to American College of Sports Medicine recommendations.
• Body mass index lower than 18.5 kg/m2 or greater than 40 kg/m2.
• Pregnancy.
• Fluency and understanding of the Spanish language.