Near the England-Wales border, over remote and craggy hillside tracks that have been re-routed to end in their back garden, three siblings ride their bikes. Not an uncommon activity, the family bike ride. The exception, in this case, being that the family have often had cause to pop each other's dislocated shoulders back into place.

Dan, Gee and Rachel Atherton are at the forefront of the breakneck world of mountain biking. Gee, 24, is the downhill world champion (he had to have his shoulder popped back in by sister Rachel after a crash last December). Dan, the eldest at 27, is a top-10 competitor who specialises in eye-catching jumps (he reset Rachel's shoulder after she rode into a truck in California in January). And Rachel, the youngest at 21, is the downhill women's world champion and winner of last year's season-long World Cup (she's still in recovery from the Californian accident). A decade of tearing down the world's mountains hasn't only made the Athertons the best biking family in the world - it has just about qualified them as freelance surgeons. "If you ever pop your shoulder," says Gee, "give us a call."

The three are at home in their Welsh cottage before the UK leg of the World Cup in Fort William on 6 June. If the 2008 season was all thrills - Gee winning the men's downhill title in June after his closest rival crashed out on the final bend, Rachel triumphing on the same day and becoming the first Brit to win the women's world title - 2009 has been more stilted. Her shoulder injury means Rachel is yet to wear the rainbow jersey she earned last year; Gee won the first race of the season but has wavered since, and needs a win in Scotland this month to reboot his title defence.

"But we bounce off hype, having everyone watching," says Gee. "And magazines tipping us for wins," says Rachel, finishing his sentence. "It's because we live way out here in the country," adds Dan, "starved of attention and affection."

They moved here, to the one-shop village of Llangynog, Powys, in 2004, buying the family home from their mother and transforming it into a bike rider's haven, with a workshop in the front room and a bike track in the garden. They convinced a local farmer to open up his land for competitions, and now riders make the pilgrimage here from all over the country. The willingness of British riders to travel so far to enjoy the terrain is one reason that we have had so much success in world competition recently, says Gee. "Because we don't have as many mountains, we have to work harder to find them and to train. In California or the south of France it's all there for you, but kids in the UK have to want it."

Dan was the first to "want it" - he bought a reluctant Gee his first BMX when they were kids so that he would have someone to ride with, and later persuaded Rachel to compete too - but he is the only one in the family not to have won a world title. "All my life I've looked out for Gee and Rach," he says. "Not necessarily a good thing as a professional athlete, because you have to be quite selfish. I'm learning to look after myself a little bit more."

Dan has had some decent results this season, but is eyeing up a grander competition. "The three of us have been approached about converting to BMX for the Olympics in London," he says. "The other two are focused on downhill, but it's been on my mind quite a lot." He'll make a decision at the end of the season; meanwhile he's getting into shape in the gym the siblings built in their garage. "I'll need bigger thighs for 2012," he says. "More like Rachel's size."

Gee guffaws, Rachel gives him a punch, and then the three grab their bikes and make for the nearest mountain. Today they will tackle a 45-degree incline of loose slate that constantly shifts under-wheel and sends sharp chips of flint shooting up at their ankles. Just another family bike ride.

• For more info, go to athertonracing.co.uk; fortwilliamworldcup.co.uk