Effects of Controlled Breathing Added to Therapeutic Exercise in Multiple Myeloma

Inclusion Criteria: * Age ≥ 18 years. * Confirmed diagnosis of multiple myeloma, currently undergoing active treatment with daratumumab, and under clinical follow-up by the Hematology Department of HU12O. * Explicit medical indication for supervised physical activity issued by the responsible hematologist and documented in the medical record. * No scheduled hematopoietic stem cell transplantation within the 60 days following the planned start date of the intervention (verified through medical record review). * Functional status of ECOG 0-2 (Eastern Cooperative Oncology Group), assessed by a healthcare professional from the Hematology Department, ensuring the ability to perform at least basic and light instrumental activities of daily living, including independent ambulation. * Access to a smartphone with stable internet connection, required for monitoring and recording adherence to the intervention. * Ability to provide written informed consent, demonstrating understanding of the study's nature, purpose, and procedures. Exclusion Criteria: * Medical risk contraindicating exercise or breathing techniques: +Clinically significant cardiovascular disease, including: decompensated heart failure, acute myocardial infarction within the past 3 months, clinically uncontrolled arrhythmias, unstable angina, acute-phase deep vein thrombosis or pulmonary embolism, pacemakers or cardiac devices whose monitoring parameters contraindicate supervised exercise according to cardiology. * Severe decompensated respiratory disease, such as acute exacerbation of COPD, severe respiratory insufficiency, or persistently low resting oxygen saturation \< 90% (not correctable). * High musculoskeletal or bone risk: * Extensive lytic bone lesions, high risk of pathological fracture, or unstable vertebral fracture, documented by imaging or based on the assessment of the Hematology/Traumatology specialist. * Uncontrolled pain that prevents safe participation in an exercise program. * Hematologic or systemic conditions contraindicating exercise: * Severe anemia: hemoglobin \< 9 g/dL in women or \< 8 g/dL in men (latest laboratory test ≤ 14 days). * Active systemic infection contraindicating exercise, fever ≥ 38 °C, or neutropenia \< 0.5 × 10⁹/L. * Severe cytopenias that, in the opinion of the hematologist, preclude moderate exercise. * Functional or procedural limitations: * Inability to remain in the supine position for ≥ 5 minutes, required for part of the breathing intervention. * Confirmed pregnancy or reasonable suspicion of pregnancy. * Severe cognitive impairment, major psychiatric disorders, or neurological diseases that limit understanding of the procedures or safe participation. * Significant difficulty understanding the language (spoken or written) that prevents following essential instructions or completing validated questionnaires.