Remote HR-guided high-intensity interval training with weekly health monitoring in breast cancer patients during chemotherapy: A moderation analysis of physiological predictors

Background: The study aimed to investigate the effects of a six-month remotely monitored heart rate – guided high-intensity interval training (HIIT) program on aerobic capacity, functional performance, and weekly self-reported health outcomes in women with stage II–III breast cancer undergoing neoadjuvant chemotherapy. Materials and methods: Fifty-six women (mean age 47 ± 8 years) were randomly assigned (1:1) to a HIIT group or a control group (CG). Thirty-five participants were included in analyses (HIIT group = 17; CG = 18). HIIT group performed 4 × 4-minute HIIT sessions at the intensity of 85–95% of the peak heart rate, two to three times weekly for six months. Aerobic capacity, time to exhaustion, functional performance, and weekly self-reported health domains were assessed before and after the intervention. Generalized linear mixed-effects models tested group × time interactions, and moderation analyses to test if physiological changes predicted self-reported trends. Results: The HIIT group achieved 79% adherence without adverse events. Peak oxygen uptake was maintained in the HIIT group (p = 0.94) but declined in CG (−13%, p < 0.001). Time to exhaustion (+5%, p = 0.043), 6-minute walking performance (+7%, p = 0.006), 30-second sit-to-stand (+19%, p = 0.003), and five-times sit-to-stand (+20%, p < 0.001) improved in the HIIT group. Significant group × time effects favored the HIIT group for physical functioning (p = 0.003), and both psychological state and sleep (p < 0.001). Reductions in the respiratory exchange ratio predicted improvements in pain, fatigue, social functioning, and sleep (all p < 0.01). Conclusion: Remote HIIT during chemotherapy preserved aerobic capacity and improved functional and patient-reported outcomes. Reductions in the respiratory exchange ratio moderated several patient-reported out-comes, suggesting an association between metabolic efficiency and less severe symptoms during chemotherapy.