From awkward-fitting uniforms to being picked last for teams, students around the world have gripes about gym class. But in China, such complaints have taken on a very particular nature, with some saying that school running tracks give them headaches and bloody noses.

Reports of so-called "toxic tracks" have simmered for months, spanning cities from Sichuan to coastal Zhejiang province. They took on a fresh urgency earlier this spring, when students in China's capital city also complained that school tracks were...