Mountain bike
Theunisse continued working with Specialized until the sponsor left the sport at the end of 2001. Theunisse then moved to Majorca, where he began riding his mountain bike 150 km a day. He won the European over-30 championship in 2002. He competed from 2003 to 2005 despite consistent pain due to spinal damage, difficulty walking straight as well as involuntary muscle or spastic attacks. Theunisse had twelve wins as an active Mountain bike cyclist. Theunisse was sponsored by PowerPlate-Giant and concentrated on the mountain bike marathons of the World and European championships.