But that’s exactly what Kevin Seaward did as part of his training for the Olympic Games in Rio, where he competed in the men’s marathon for the Ireland team.
Mr Seaward, 31, who is assistant head at The Martin High School in Anstey, Leicestershire, and also teaches PE, completed the marathon in two hours 20 minutes, finishing in 64th place.
He was disappointed with his time, which was six minutes slower than his personal best, but suffered a serious two-day bout of flu just before the event. Even so, he was determined to carry on.
“It would have been easy for me to stop, and a lot of people did, but the students inspired me,” he said. “We always tell pupils to persist and continue to work hard when things get tough or don’t go their way and I kept thinking about that message while I was running.”
Mr Seaward excelled as an athlete from a young age but only took up marathon running two years ago. He ran the Berlin marathon last year in two hours, 14 minutes and was selected for Ireland’s Olympic team.
Staff and students at The Martin High School took a keen interest in his Olympic training. All 850 pupils took part in the 2016 Sport Relief Road to Rio Challenge, each running at least a mile in PE lessons to represent the distance between Anstey and Rio.
Support: Olympian Kevin Seaward (right) with his colleagues on the playing fields of The Martin High School
Many of them watched the men’s marathon live on television and on the day of the race the school tweeted: “Congratulations to Mr Seaward. Completing the Olympic marathon in just 2:20:06. The Martin High School community are so proud of you.”
Mr Seaward met a host of world-famous athletes in Rio, including Usain Bolt and Mo Farah. He also visited a primary school in Uberlândia, 1,000km from Rio, where the Irish holding camp was based.
Now term has started, he is busy planning assemblies at his own school and at local primaries.
“I am very driven in both my careers,” he said. “I work very hard in school and I work very hard with my running too.”
Mr Seaward wasn’t the only Martin High School representative at the Rio Olympics. Lizzie Warner, a talented year 11 archer, was there as part of Team GB’s Ambition Programme for athletes aspiring to compete at the 2020 Olympics in Tokyo.