Effects of an Individualized, Smartwatch-Supported Exercise Intervention on Physical Activity, Cardiorespiratory Fitness, Limb Function and Quality of Life in Adolescent and Young Adult Survivors of Bone and Soft Tissue Sarcoma: A Randomized Controlled Trial (Sport Ist Herzenssache)

Survivors of pediatric and adolescent bone and soft tissue sarcomas frequently experience long-term sequelae including reduced muscle strength, impaired joint mobility, and diminished cardiorespiratory fitness, often resulting from multimodal oncological therapy (surgery, chemotherapy, radiotherapy). These sequelae contribute to persistently low levels of physical activity compared to healthy peers, which in turn is associated with an elevated risk of cardiovascular disease-a risk already increased 2- to 10-fold in this population due to cardiotoxic treatment exposure (e.g., anthracyclines, thoracic irradiation). Despite established benefits of physical activity in reducing fatigue, improving quality of life, and lowering cardiovascular morbidity, structured exercise programs are not yet routinely integrated into long-term follow-up care for sarcoma survivors.

This monocentric, randomized controlled trial ("Sport ist Herzenssache") aims to evaluate the effectiveness of an individualized, partially supervised, digitally supported exercise intervention in increasing moderate-to-vigorous physical activity (MVPA) among adolescent and young adult (AYA) survivors of bone and soft tissue sarcoma during routine oncological follow-up care.

Eligible participants are aged 15-39 years, have completed local tumor therapy (surgery and/or radiotherapy) more than 12 months prior to enrollment, and are receiving follow-up care at the Sarcoma Center of the University Hospital Essen. Following informed consent, participants will be randomized 1:1, stratified by tumor location (lower extremity/pelvis, thorax, other), into two groups: (1) a control group receiving a wearable activity tracker (Garmin Venu® Sq 2) for self-monitoring, and (2) an intervention group receiving the same wearable device plus an individualized, partially supervised home-based exercise program over 8 weeks, combining endurance/cardio training (60 min/week) and strength/aerobic sessions (3 × 30 min/week), in accordance with WHO physical activity recommendations and exercise guidelines for cancer survivors. Supervised sessions are delivered via video conferencing by trained exercise therapists.

Physical activity is monitored continuously via wearable device across a total observation period of approximately 13-15 weeks in both groups. At baseline and after the observation period, participants undergo a comprehensive assessment including functional mobility testing (Timed Up and Down Stairs, Timed Up and Go, 6-Minute Walk Test, modified Clinical Test of Sensory Interaction in Balance), goniometry, handheld dynamometry, and cardiopulmonary evaluation (spiroergometry, echocardiography, 12-lead ECG). Patient-reported outcomes include health-related quality of life, cancer-related fatigue, physical functioning, and self-rated health status.

The primary endpoint is average daily MVPA (minutes/day), measured objectively via wearable device. Secondary endpoints include cardiorespiratory fitness (VO2max), cardiovascular risk factors, orthopedic function, and patient-reported quality of life and fatigue. Exploratory analyses will examine correlations between MVPA and physical/psychosocial outcomes, as well as associations with physical activity levels during acute cancer therapy.