For a special group of runners, the "hell mode" BMW Hood to Coast China Relay offers both a chance to test their limits and help heal the wounded.

A growing number of altruistic Beijing physicians are becoming regular participants in all sorts of marathons, both as runners and health professionals safeguarding the rest of the field.

Going by the name of Beijing Doctors Runners (BDR), they kept watchful eyes on the Hood to Coast Relay for the second time on the weekend, although a quick-response medical team was already in place to provide aid when needed.

"We sent more people to join the Hood to Coast this year than last time," said Zhang Zengqi, vice-captain of one of the BDR teams to brave the race. "Last year, we had two teams in the Hood to Coast, but this year the number jumped to five teams. And we had unified cars for all five.

"We are not just runners; we use our experience to help whoever is in need. Before we come here, we organized first-aid training for our runners, who are also doctors or nurses."

Since its formation in 2015, BDR has amassed 827 members, with 407 of them possessing MD degrees. The group has participated in over 109 long-distance running events, during which they have administered aid to 8,000 runners.

The group has received awards from the General Administration of Sport of China and the Chinese Athletic Association.

"We started the group because we realized lots of runners run with passion but not necessarily sensibly," Zhu Xishan, leader of the group and a doctor at Peking University First Hospital, told China Daily.

"Emergencies like cardiac arrest are very common in marathons. We are all trained physicians so we thought, 'Why not combine our profession and our passion for marathons?'"

Apart from providing medical attention, the group promotes a healthy and scientific style of running. BDR's message to the public is simple: Be wary of pushing your body too hard.

"Not everyone is suited to running marathons, especially those who have cardiovascular diseases," said Zhang.

"It differs from runner to runner. Also some people run in the wrong style, which can harm their body. Running a marathon is unhealthy if your body is not suited for it."