Low Versus Moderate Intensity Aerobic Exercises on Bone Mineral Density in Breast Cancer Patients Undergoing Radiotherapy: A Randomized Controlled Trial

Abstract

Background: Breast cancer is one of the most common malignancies affecting women, and improved survival has increased attention to treatment-related complications that may influence long-term health. Anticancer treatment can adversely affect the skeleton through ovarian dysfunction, estrogen deprivation, endocrine changes, reduced physical activity, and alterations in body composition and bone remodeling. Declining bone mineral density (BMD) is clinically important because it may contribute to osteopenia, osteoporosis, and future skeletal morbidity. Exercise is recommended as part of breast-cancer rehabilitation, and weight-bearing aerobic activity provides repeated mechanical loading and muscle-generated forces that may support bone formation and preservation. However, skeletal adaptation may differ according to exercise intensity and anatomical site, and direct evidence comparing low- and moderate-intensity aerobic exercise during radiotherapy remains limited. Purpose: To compare the effects of low- and moderate-intensity supervised aerobic treadmill exercise with a control condition on BMD in women with breast cancer undergoing radiotherapy. Subjects and Methods: Sixty-six women with stage I-III breast cancer were randomized equally to Low-intensity, Moderate-intensity, and Control groups (22/group). The Low-intensity group exercised at 35-60% of age-predicted HRmax and the Moderate-intensity group at 65-75% HRmax, four times weekly for 12 weeks. All groups received the same approximately 15-minute standardized physical therapy program (range-of-motion exercises, stretching, and strengthening exercises), while the Control group received this program without additional treadmill exercise. Areal BMD was measured by DXA at L1-L4, femoral neck, total hip, and 33% radius before and after the 12-week intervention; lumbar-spine BMD was the primary outcome. A mixed-design MANOVA evaluated time, treatment, and treatment-by-time effects, followed by Bonferroni-corrected comparisons. Results: A significant treatment-by-time interaction was observed (Wilks' Λ=0.18, F (8,120) =20.24, p<0.001, partial η²=0.57). BMD increased significantly at all measured sites in both exercise groups, while no significant changes occurred in the Control group. The Moderate-intensity group had significantly higher post-treatment BMD than both the Low-intensity and Control groups at L1-L4, femoral neck, and total hip; no significant between-group difference was observed at the 33% radius. Lumbar-spine BMD increased by 3.57%, 10.08%, and 1.70% in the Low-intensity, Moderate-intensity, and Control groups, respectively. Conclusion: Moderate-intensity treadmill exercise produced a greater BMD response than low-intensity exercise at the lumbar spine, femoral neck, and total hip, supporting a site-specific skeletal response.