REstoring Metabolic FLEXibility Through Combined Exercise in Breast Cancer Survivors: A Randomized Controlled Trial.

The REFLEX study is a randomized, controlled clinical trial designed to evaluate the impact of a 16-week supervised, combined exercise program on metabolic flexibility and cardiorespiratory fitness in breast cancer survivors. While cancer treatments have significantly improved survival rates, the disease and its therapies often cause systemic mitochondrial dysfunction and muscle loss. This leads to persistent "metabolic inflexibility"-a reduced ability to efficiently switch between burning carbohydrates and fats for energy. This inflexibility, exacerbated by sedentary behavior and cancer-related fatigue, can severely diminish a patient's functional autonomy and overall quality of life. The trial focuses on assessing whether exercise can restore this metabolic adaptability in women aged 18 to 70 with stage I-III breast cancer who are currently on hormonal treatment and completed neo/adjuvant chemotherapy within the past 6 months. The study operates on the primary hypothesis that an individualized exercise intervention will significantly improve the participants' metabolic flexibility-measured via the metabolic crossover point-and overall aerobic capacity (VO2max) when compared to a control group. Additionally, the trial will analyze secondary outcomes, including changes in cardiovascular and metabolic risk factors, muscle strength, body composition (such as bone mineral density), and patient-reported outcomes assessing quality of life, fatigue, joint pain, anxiety, and depression. A total of 44 participants will be randomly assigned to either the intervention or control group. Participants in the intervention group will complete a 16-week program consisting of two weekly supervised sessions. Each session lasts between 55 and 85 minutes and includes a tailored combination of aerobic and strength training based on the individual's baseline fitness and metabolic thresholds. Participants in the control group. will receive standard educational materials via email, featuring healthy lifestyle and exercise guidelines from the World Health Organization (WHO) and the American College of Sports Medicine (ACSM). To evaluate the program's effectiveness, comprehensive medical and functional assessments will be conducted at baseline, immediately after the 16-week intervention, and at a 3-month follow-up. These evaluations include submaximal and maximal exercise tests on a cycle ergometer to analyze respiratory gases, detailed blood tests, body composition imaging (DXA scans), and maximum dynamic strength testing. Ultimately, the research aims to generate high-quality evidence to optimize standard exercise recommendations for breast cancer survivors and improve their long-term health and resilience.

Sex

Female

Minimum age

18 Years

Maximum age

70 Years

Inclusion Criteria:

* Women aged between 18 and 70 years.
* Confirmed diagnosis of breast cancer in stages I to III.
* Received neo-adjuvant or adjuvant chemotherapy and completed the chemotherapy treatment within the 6 months prior to study enrolment.
* Residency within a distance of less than 40 km from the Hospital Universitario de Toledo.

Exclusion Criteria:

* Diagnosis of stage IV breast cancer.
* Undergone major surgery within the 4 months prior to enrolment or scheduled for breast reconstruction surgery during the study period.
* Diagnosis of diabetes mellitus with poor glycaemic control, defined as an HbA1c value greater than or equal to 8.5%.
* Presence of an acute infectious disease.
* Absolute or relative medical contraindications for physical exercise or maximal exercise stress testing, according to the American College of Sports Medicine (ACSM) guidelines.
* Serious cardiac or cardiovascular disease, including a history of myocardial infarction, heart failure, or known cardiomyopathy.
* Regular consumption of beta-blockers or any medication that alters the functioning of the nervous system.
* Currently active, defined as engaging in more than 150 minutes per week of structured physical exercise during the 6 months prior to enrolment.