Which Exercise Prescriptions Improve Physical Fitness in Patients with Breast Cancer Before, During, and Following Treatment? A Systematic Review and Meta-analysis of Randomized Controlled Trials

BACKGROUND: Exercise is now recognized as an essential component of the cancer care continuum. However, the optimal exercise prescriptions to improve physical fitness in breast cancer remain under debate. OBJECTIVES: In a systematic review and meta-analysis of randomized controlled trials (RCTs), we investigated how exercise affects muscular strength, fat-free mass, functional exercise capacity (FEC) and cardiorespiratory fitness during pretreatment, active treatment, and post-treatment for breast cancer. We also investigated how exercise mode, frequency, intensity, supervision, and duration of intervention affect breast cancer survivors' physical fitness. METHODS: We searched four electronic databases to identify RCTs examining exercise's effects on muscular strength, fat-free mass, functional exercise capacity, FEC, and cardiorespiratory fitness in women with breast cancer. We calculated pooled effects (SMD) using the software Comprehensive Meta-Analysis. Subgroup analyses were conducted based on phases of cancer care and exercise mode, frequency, intensity, supervision, and duration of intervention. RESULTS: Across 68 randomized controlled trials (N = 4,158), exercise significantly increased muscular strength (Hedges' g = 0.66, 95% CI 0.46-0.85), FEC (Hedges' g = 1.04, 95% CI 0.56-1.52), cardiorespiratory fitness (Hedges' g = 0.96, 95% CI 0.45-1.47), and fat-free mass (Hedges' g = 0.12, 95% CI 0.03-0.20). However, these effects varied according to the phase of cancer care and exercise prescription characteristics, including modality, frequency, supervision, intensity, and duration. During active treatment, combined exercise significantly improved muscular strength, FEC, and cardiorespiratory fitness, but not fat-free mass. In contrast, post-treatment exercise significantly enhanced muscular strength, fat-free mass, and FEC, with no significant effect on cardiorespiratory fitness. Data for evaluating exercise's pretreatment effects were insufficient. The greatest improvements across outcomes were observed with supervised combined aerobic-resistance exercise programs performed at least three times per week for a minimum of 12 weeks. CONCLUSIONS: Although exercise improves breast cancer survivors' physical fitness, its effects differ depending on its mode, frequency, intensity, supervision, and total duration in addition to the phase of cancer care.