Purpose: Despite a paucity of evidence, prevention guidelines typically advise avoidance of heavy lifting in an effort to protect against breast cancer-related lymphedema. This study compared acute responses in arm swelling and related symptoms after low- and heavy-load resistance exercise among women at risk for lymphedema while receiving adjuvant taxane-based chemotherapy. Methods: This is a randomized, crossover equivalence trial. Women receiving adjuvant taxane-based chemotherapy for breast cancer who had undergone axillary lymph node dissection (n = 21) participated in low-load (60%-65% 1-repetition maximum, two sets of 15-20 repetitions) and heavy-load (85%-90% 1-repetition maximum, three sets of 5-8 repetitions) upper-extremity resistance exercise separated by a 1-wk wash-out period. Swelling was determined by bioimpedance spectroscopy and dual-energy x-ray absorptiometry, with breast cancer-related lymphedema symptoms (heaviness, swelling, pain, tightness) reported using a numeric rating scale (0-10). Order of low- versus heavy-load was randomized. All outcomes were assessed before, immediately after, and 24 and 72 h after exercise. Generalized estimating equations were used to evaluate changes over time between groups, with equivalence between resistance exercise loads determined using the principle of confidence interval inclusion. Results: The acute response to resistance exercise was equivalent for all outcomes at all time points irrespective of loads lifted, with the exception of extracellular fluid at 72 h after exercise with less swelling after heavy loads (estimated mean difference, -1.00; 95% confidence interval, -3.17 to 1.17). Conclusions: Lowand heavy-load resistance exercise elicited similar acute responses in arm swelling and breast cancer-related lymphedema symptoms in women at risk for lymphedema receiving adjuvant taxane-based chemotherapy. These represent important preliminary findings, which can be used to inform future prospective evaluation of the long-term effects of repeated exposure to heavy-load resistance exercise.