Resistance Training and Lymphedema in Breast Cancer Survivors.

Importance: Lymphedema is a common treatment-related adverse effect among breast cancer survivors that can limit activity and mobility. Although exercise is associated with improved outcomes after breast cancer treatment, data are limited on the association of intense physical activity, including strength training, with lymphedema. Objective: To examine the association between resistance training and lymphedema among breast cancer survivors. Design, Setting, and Participants: In this cohort study conducted between September 15, 2022, and March 26, 2024, women from 3 prospective studies (EXERT-BC, EXERT-BCN, and EXERT-C) underwent thrice-weekly, dose-escalated resistance training for 3 months to promote strength, mobility, and hypertrophy. Main Outcomes and Measures: Lymphedema was assessed at baseline and completion using bioimpedance analysis to evaluate fluid and body composition metrics, distinguishing among intracellular water, extracellular water, and total body water. Results: A total of 115 women completed the exercise regimen (median age, 54 years; range, 24-71 years). Ninety-six participants (83%) underwent sentinel lymph node biopsy, whereas 14 (12%) underwent axillary lymph node dissection. At baseline, 15 women (13%) had clinical lymphedema: 8 (8%) in the sentinel lymph node biopsy group and 7 (37%) in the axillary lymph node dissection group. No participants experienced subjective or clinical worsening of lymphedema after completing the exercise regimen. Bilateral arm lean mass significantly increased after resistance training (affected arm: median [IQR], 5.64 [4.98-6.20] lb; 95% CI, 5.40-5.84 lb) vs baseline (median [IQR], 5.45 [4.92-6.08] lb; 95% CI, 5.34-5.67 lb) (s = 1789.5; P < .001). The edema index (extracellular water to total body water ratio) significantly improved in all patients, signifying a reduction in lymphedema at the completion of exercise (mean, 0.383; 95% CI, 0.382-0.385) compared with baseline (mean, 0.385; 95% CI, 0.384-0.386) (t110 = 4.05; P < .001). CONCLUSIONS AND RELEVANCE: In this cohort study of breast cancer survivors, intense resistance training did not exacerbate lymphedema and was associated with improvements in fluid balance and lean mass in the upper extremities. These findings suggest support for the inclusion of structured resistance exercise as part of breast cancer treatment and survivorship care.