A paradigmatic “portrait” documentary—the popular sort that eschews cultural information and risk to focus on “how it feels” to be its subject—Yung Chang’s film visits a pair of Sichuan Province boxing trainers employed by the state to examine a sea of grade-schoolers for potential Olympic contenders. (They can be famous, the kids are told. “If you don’t train hard, then you’ll only be your mama’s kid.”) Chang eventually settles on two fierce-browed contenders in their teens, and on one of the trainers, soulful 30-ish Qi Moxiang, who hasn’t yet given up his own hopes for a Tysonesque pro career. Like so much else in China, the system is mercenary and cruel to children, but Chang falls into a repetitive training/advice/meal scene structure that’s less than revelatory, and the bouts are so blurrily filmed and so leavened with reaction shots that you can’t really see what’s going down. In the end, once we realize the title doesn’t refer to these bantams’ weight class but to their strength of heart, or something, the film feels blandly respectful and, oddly enough, apolitical.