Willoughby posted an Instagram video on Tuesday, showing him on an exercise bike.
While the 25-year-old shifted unsteadily at times on the bike seat and occasionally needed support from a helper, the BMX ace simulated a standing start in a track race.
"Anyone need a starter for Tokyo #notquitedoneyet #getupyoudog #biggears," Willoughby wrote.
It is a far cry from September last year when Willoughby had a horrific fall while training on a BMX track in the United States.
The impact initially left the London Olympics silver with no movement from the chest down, after he sustained fractures to vertebrae that severely compressed his spinal cord.
Willoughby and American BMX star Alise Post will marry on December 31 and he has vowed to be walking at the ceremony.