This study aims to apply autologous differentiated myocyte subcutaneous transplantation in patients with muscle atrophy to explore its safety, feasibility, and efficacy.

For patients with muscle atrophy caused by multiple conditions leading to long-term bed rest, there is currently a lack of effective clinical strategies that can reverse or delay muscle atrophy and functional decline. Conventional rehabilitation training and nutritional support show limited benefit for muscle atrophy induced by prolonged immobilization, and new interventions are urgently needed. Based on our prior experimental findings, we have developed an autologous differentiated myocyte subcutaneous transplantation technique. This approach allows long-term survival of the graft in vivo, mimics a state of "continuous exercise," and provides stable secretion of myokines. Through these mechanisms, it systemically improves muscle quality, bone mineral density, energy metabolism, and inflammatory status.

This study aims to innovatively translate autologous differentiated myocyte subcutaneous transplantation to human application, with the goal of constructing a sustainable, spontaneously contractile, and endocrine-functional "muscle graft." The study objectives are as follows: (1) to verify graft survival, vascularization, and immune tolerance after autologous differentiated myocyte subcutaneous transplantation in patients with long-term bed rest-related muscle atrophy, and to ensure the safety of clinical application; (2) to systematically evaluate the effects of the graft on skeletal muscle mass, muscle strength, and exercise endurance, and to explore its potential to reverse muscle atrophy and preserve muscle function; and (3) to analyze the regulatory effects of graft-derived myokines on systemic energy metabolism, bone mineral density, and chronic inflammatory status, and to assess their impact on aging-related degenerative changes, including sarcopenia, osteoporosis, and metabolic disorders.

Inclusion Criteria:

1. History of long-term bed rest: continuous bed rest for ≥4 weeks, with causes including neurological injury (such as brain death, stroke, or spinal cord injury), recovery after major orthopedic surgery, intensive care unit stay, or activity limitation due to chronic diseases.
2. Evidence of muscle atrophy: a significant reduction in muscle mass or muscle strength confirmed by clinical assessment and imaging. According to dual-energy X-ray absorptiometry (DXA), appendicular skeletal muscle mass index (ASM/height²) < 7.0 kg/m² in men and < 5.4 kg/m² in women, in accordance with EWGSOP2 criteria.
3. Stable underlying medical conditions, with no acute exacerbation, and an APACHE II score of 0-20.
4. Absence of severe comorbidities that would contraindicate surgical or transplantation interventions.
5. Written informed consent obtained from the patient, an immediate family member, or a legal guardian, agreeing to muscle biopsy, with general health status adequate to permit subcutaneous transplantation.

Exclusion Criteria:

1. History of malignant tumors.
2. Coagulation disorders or current use of anticoagulant therapy.
3. Active infection or immunodeficiency.
4. Severe cardiac or renal insufficiency (estimated glomerular filtration rate < 60 mL/min/1.73 m²; New York Heart Association [NYHA] class III-IV heart failure).
5. Muscle-related diseases, including hereditary myopathies (such as muscular dystrophy) or acquired myositis (creatine kinase > 3 times the upper limit of normal).
6. Severe local skin lesions or a history of allergic reactions at the injection site.
7. Use of muscle growth-modulating medications (such as testosterone or growth hormone) within the past 6 months.
8. Long-term use of corticosteroids or immunosuppressive therapy, including anti-rejection medications following organ transplantation.
9. Other exclusion criteria: participation in other interventional clinical trials (excluding observational studies).
10. Any other medical or ethical conditions deemed by the investigator to make the participant unsuitable for enrollment.

Individual participant data will not be shared at this stage.