Walker, 23, won the world title in 2007 and 2009, finished fourth in the Beijing Olympics and was overall World Cup champion last year, so she's among the top echelon.
She suspects she surprised some of her main rivals at Birmingham, given that her injury, suffered in a Supercross event in Norway, should have sidelined her for the worlds, or at least significantly dimmed her abilities.
"They all knew I was coming back from injury, but to be right up next to them probably gave them a bit of a shock," she said.
While Willers is staying in the US before the Games, Walker is training in Cambridge until the end of the month before heading to the Netherlands where there is an Olympic replica track, and then Copenhagen, venue for last year's worlds, to fine-tune preparations.
Riders had three days to test out the Olympic track before the worlds in Birmingham, although her injury restricted Walker to "rolling around" the circuit.
She likes the track which she rates as bigger and more technical than that used in Beijing where the sport made its Olympic debut. Walker got a second placing on it in a World Cup last year and rates it a good spectator venue, with straights wide enough to offer more passing opportunities rather than a procession, once the duel to the first corner is resolved.
Willers returns for a second Games after finishing 23rd in Beijing and was seventh in the world champs last month, while 21-year-old Pickard is the new face on the team.
Hanlen, a Whakatane physiotherapist, took up mountainbiking only in 2010. She had been locked in a duel for the one spot with Rosara Joseph until the 2008 Olympian broke her wrist just before a World Cup race in France last month.
BOUND FOR LONDON
BMX: Sarah Walker (Cambridge), Marc Willers (California-based), Kurt Pickard (Tauranga)
Mountainbiking: Karen Hanlen (Whakatane).