Oscar and Otis Burgess from Ranmoor recently reached a combined total of 350 parkruns between them at Endcliffe parkrun.
The free 5km run is held in parks around the world every Saturday at 9am.
High Storrs Year 11 pupil Oscar, aged 16, marked run number 250 on April 30 with an impressive time of 16.50 – nine seconds off his personal best.
He achieved 10 personal bests in as many weeks last year on his way to becoming a sub-17 parkrunner.
Meanwhile, Otis, 11, who attends Nether Green Junior School, ran a PB of 23.14 in his hundredth event on March 26.
He has since beaten that time by almost one minute, completing the Rother Valley course in 22.22.
“I am so proud of both boys,” said their dad Richard.
"Oscar is miles ahead of me nowadays and Otis will soon be quicker than me.”
Oscar began taking part in parkrun aged seven, while Otis has been running at the event since he was five.
"It’s actually the kids that drag us to it now,” said Richard, who also runs along with the boys’ mum Helen.
He added: “The events really do generate a big sense of community.
"You are not really friends with any of the people outside of seeing them on a Saturday morning at the park, but you chat to all these people as lifelong friends.”
Six parkrun events take place in Sheffield every week – Concord, Endcliffe, Graves, Hillsborough, Millhouses Park and Sheffield Castle.