This study aims to investigate the feasibility of a prehabilitative training intervention. The intervention includes specific strength and balance exercises during neoadjuvant chemotherapy with children and adolescents diagnosed with soft tissue or bone tumor in the lower extremity. This explorative approach of prehabilitation might help to reduce muscle and bone weakening and associated functional limitations during and after acute therapy. By designing this study like a controlled clinical trials, the investigators will also gather preliminary data on the intervention's potential effects in enhancing/on the pre-operative condition. The goal is to improve post-operative outcome and rehabilitation processes in children and adolescents diagnosed with soft tissue or bone sarcoma of the lower extremity.

Soft tissue and bone sarcomas of the lower extremity pose significant challenges for affected individuals, often associated with considerable burden. Chemotherapy, load restrictions, and surgery frequently result in long-term physical limitations, causing structural and functional deterioration. In childhood and adolescence, these challenges are particularly pronounced, as they affect physiological development, resilience, and autonomy. Although movement promotion and therapeutic programs are designed to address these deficits, they are typically implemented post-operatively and during follow-up care. The benefit of implementing a specific program before the operative therapy remains elusive. The presented study explores the feasibility of a supervised prehabilitative training intervention and gather preliminary data on its potential effects in enhancing the pre-operative condition. The goal is to improve post-operative outcome and rehabilitation in children and adolescents diagnosed with soft tissue or bone sarcoma of the lower extremity.

This bicentric feasibility study, designed as a controlled clinical trial, enrolls all children and adolescents aged 6-18 years who are newly diagnosed with primary osteosarcoma, Ewing's sarcoma, or rhabdomyosarcoma of the lower extremity. Based on the study site, participants are allocated to either the intervention group (IG) or control group (CG), with a target sample size of 16-18. The intervention consists of specific strength and balance training sessions during neoadjuvant therapy, conducted at least twice a week for a minimum of 30 minutes per session. The CG does not receive any training intervention. The study has been consented by the local ethics committee.

The primary endpoint is the proof of feasibility of the intervention, assessed via descriptive analysis of recruitment rate, acceptance, data quality, practicability, and safety (adverse events). The secondary endpoint is the demonstration of the efficacy of the intervention comparing structural and functional measurements intra-individually and between groups at four timepoints: within ten days post-diagnosis, pre-operatively (post-intervention), at the end of therapy, and at 1-year follow-up. The measurements include psoas muscle area, body composition, strength, mobility, balance ability, gait analysis, two questionnaires on physical activity and quality of life, and quantitative measures of the clinical course during treatment (days of hospitalization, infection rates, etc.).

This study is designed to evaluate the feasibility of a specific prehabilitative training intervention in children and adolescents with soft tissue or bone sarcoma of the lower extremity. Additionally, preliminary data on the effects of this training are collected, aiming to mitigate muscle mass loss, support physiological body composition, and improve functional outcomes such as balance, gait, and physical activity. Enhancing everyday functionality and fostering a sense of autonomy can significantly improve the quality of life in this population, underscoring the importance of investigating and promoting such interventions in this underrepresented patient group.

Inclusion Criteria:

• Diagnosis of a bone tumor or soft tissue sarcoma of the lower extremity
• Diagnosed less than 10 days ago, confirmed through biopsy
• Age Range of 6 to 18 years
• Treatment will be conducted at one of the two designated study sites

Exclusion Criteria:

• Medical contraindications for the implementation of the intervention and measurements, in consultation with the treating physicians (e.g., acute risk of bleeding or fractures, pain, infection, nausea, dizziness, lack of orthopedic clearance for weight-bearing in the tumor region, other acute orthopedic limitations unrelated to the underlying condition, etc.)
• Language barriers that prevent understanding of the instructions for study participation
• Cognitive impairment or developmental delay that hinders comprehension of the instructions in the testing situation, thereby preventing standardized diagnostic data collection and intervention