The actor, 60, signed up to the running, cycling and swimming endurance challenge as part of business mogul Sir Richard Branson's celebrity team in August (12).
Hasselhoff left himself only three weeks to get in shape for the brutal sporting event, but it's emerged he has done a lot more work than British pop star Burke.
The actor proudly tweeted an image of himself on a hilltop, looking trim in sportswear and holding a mountain bike over his shoulder, alongside the message, "Training hard 4 (for) TheLondonTri! Looking forward 2 (to) competing w/ (with) my teammates richardbranson & alexandramusic."
But Burke then sheepishly revealed her lack of preparation for the gruelling race, writing back, "LondonTri - gonna (going to) be a lot of fun! Although I haven't really trained! I'm excited! X."