Two 14-year-old Chinese boys reportedly died early this month after running while wearing masks during physical education classes in China, New York Post reports. The boys died one week apart and one of the teens’ father told an Australian Outlet 7News that the teenager who died on  April 24 at Dancheng Caiyuan Middle School in Henan province fell backwards while running wearing a mask:

He was wearing a mask while lapping the running track, then he suddenly fell backwards and hit his head on the ground. I suspect it was because he was wearing a mask, it couldn’t have been comfortable wearing a mask while running

Cao Lanxiu, professor at Shaanxi University of Chinese Medicine has said wearing a mask was not likely to cause the boy’s death but he cannot be sure since an autopsy was not performed.

Barely a week later another student at Changsha’s Xiangjun Future Experimental School in Hunan province dropped dead according to the same publication, He was reportedly wearing an N95 respirator and running a 1,000-meter exam when he collapsed to his death. Schools in Tianjin and Shanghai have so far cancelled all physical education exams.

More: New York Post