The benefits of physical exercise at both an individual and societal level are well understood and well researched. Less well understood is how organizations can most effectively support adult physical activity in the workplace through programme design and promotion. This paper reports research on the motivation for adult participants' involvement in the 2007 Step It Up Challenge (SIUC), a team-based workplace activity programme. The strongest motivation for participation in SIUC related to the fitness and health benefits (extrinsic). There was also a strong significant relationship between high exercise performance and enjoyment of physical activity as an intrinsic motive. This research segmented adult exercisers according to motivational and behavioural characteristics in order to refine customer-orientated marketing strategies, especially promotion strategies. More definitive research into the interaction between motivation and promotion is essential to ensure high take up rates for and adherence to work-based activity programmes, particularly among adult employees.