They subject themselves to additional regulations and medical screenings to participate in school sports. "Somewhat like adults who choose to participate in a 'closely regulated industry,' students who voluntarily participate in school athletics have reason to expect intrusions upon normal rights and privileges, including privacy."
Students who participate in school sports are subject to extra rules and health checks. This situation is similar to individuals who choose to work in a profession with strict controls, implying that students should expect some restrictions on their rights and liberties, including privacy.