HIIT vs HIIT plus Plyometric Jump Training on Achilles Tendon Mechanical Properties in Youth with Obesity During Biological Maturation

Context: The worldwide prevalence of youth with obesity increased 4.2-fold between 1976 and 2022. Obesity may negatively alter the muscle-tendon unit architecture, function, and oxidative capacity. High-intensity interval training (HIIT) combined with plyometric jump training may attenuate the structural and everyday activities impairments (e.g., jumping) induced by obesity, but the effects may be moderated by biological maturation. Objective: This randomized controlled trial (RCT) protocol aims to determine the effects of HIIT and HIIT plus plyometric jump training on the muscle-tendon architecture, function, and oxidative capacity of youth with obesity across different biological maturation stages. Design: Parallel group RCT. Setting: Public health hospital, targeting time-efficient protocol training with direct application into clinical practice in the youth with obesity. Participants: Youth with obesity pre- and post-age to peak-height velocity (APHV). Intervention: Forty participants will be randomized into four equal groups: i) obese pre-APHV performing HIIT, ii) obese pre-APHV performing HIIT plus plyometrics, iii) obese post-APHV performing HIIT, and iv) obese post-APHV performing HIIT plus plyometrics. Training will last 12 wk, three times per week. The HIIT groups will complete 2 wk of familiarization with moderate-intensity continuous training, followed by 20-min HIIT sessions (85%:50% maximal heart rate) from weeks 3 to 12. The combined groups will follow the same familiarization, then progress to 15-min HIIT plus 5 min of all-out plyometric exercises. Main Outcome Measure: Achilles tendon mechanical properties will be the main outcome. The secondary outcomes will be Achilles tendon structure, gastrocnemius medialis architecture, plantar flexor muscle function, jump capacity, muscle oxidative capacity, inflammatory markers, hematological parameters, body composition, quality of life, physical literacy, and enjoyment. Conclusion: This RCT emphasizes the development of time-efficient training protocols for youth with obesity tailored to biological maturation stages.