In a world where childhood obesity is measured by scales that cannot see what lies beneath, researchers in Hong Kong are asking a quieter and more consequential question: not how much a child weighs, but what that weight is made of. A 16-week trial at Hong Kong Baptist University is testing whether plyometric high-intensity interval training — rope-skipping and progressive jumping circuits delivered inside ordinary school walls — can help children shed fat while holding onto the metabolic muscle that protects them long after the program ends. The stakes are larger than any single study: if the