Abstract Background In an effort to reduce the risk of breast cancer-related arm lymphedema, patients are commonly advised to avoid heavy lifting, impacting activities of daily living and resistance exercise prescription. This advice lacks evidence, with no prospective studies investigating arm volume changes after resistance exercise with heavy loads in this population. The purpose of this study is to determine acute changes in arm volume after a session of low- and heavy-load resistance exercise among women undergoing adjuvant chemotherapy for breast cancer at risk for arm lymphedema. Methods/Design This is a randomized cross-over trial. Participants: Women receiving adjuvant chemotherapy for breast cancer who have undergone axillary lymph node dissection will be recruited from rehabilitation centers in the Copenhagen area. Intervention: Participants will be randomly assigned to engage in a low- (two sets of 15â 20 repetition maximum) and heavy-load (three sets of 5â 8 repetition maximum) upper-extremity resistance exercise session with a one week wash-out period between sessions. Outcome: Changes in extracellular fluid (L-Dex score) and arm volume (ml) will be assessed using bioimpedance spectroscopy and dual-energy x-ray absorptiometry, respectively. Symptom severity related to arm lymphedema will be determined using a visual analogue scale (heaviness, swelling, pain, tightness). Measurements will be taken immediately pre- and post-exercise, and 24- and 72-hours post-exercise. Sample size: A sample size of 20 participants was calculated based on changes in L-Dex scores between baseline and 72-hours post exercise sessions. Discussion Findings from this study are relevant for exercise prescription guidelines, as well as recommendations regarding participating in activities of daily living for women following surgery for breast cancer and who may be at risk of developing arm lymphedema. Trial registration Current Controlled Trials ISRCTN97332727 . Registered 12 February 2015.