Arm-Strengthening Intervention Program During Radiation Treatment in Breast Cancer: A Prospective Cohort Study

Introduction: Radiation therapy is a critical component of breast cancer treatment; however, it is frequently accompanied by a decline in shoulder strength and function that can impair daily activities and limit long-term recovery. Although exercise can improve physical function and quality of life, uncertainty remains regarding the optimal timing and specificity of programs that target shoulder outcomes. This study evaluated the effects of a 6-week shoulder-strengthening intervention delivered concurrently with radiation therapy, hypothesizing that early exercise would mitigate declines in arm strength, range of motion (ROM), and muscle activation. Methods: Twenty-seven patients undergoing radiation therapy were enrolled, with 13 assigned to the exercise group and 14 to the standard-care control group. Shoulder health indicators, including shoulder muscle activation, arm strength, and ROM, were assessed at baseline, midpoint, and endpoint. A linear mixed-effects model with time × group × movement × muscle as fixed effects and group as a random intercept was used. A mixed-model analysis of variance was used to examine differences across time points, with significance set at P < .05. Tukey–Kramer post hoc tests were used to compare groups at each time × movement × muscle combination. Results: No significant between-group differences were observed in muscle activation; however, the exercise group demonstrated consistently greater arm strength with significant improvements in flexion and abduction at the midpoint. The ROM effects were smaller, although the endpoint abduction improved significantly in the exercise group. Conclusions: Early targeted strengthening during radiation therapy preserved shoulder function and mitigated treatment-related decline.