  Regular physical activity is crucial for reducing the risk of
non-communicable disease (NCD). With NCDs on the rise globally, there is an
urgent need for effective health interventions, with chatbots emerging as a
viable and cost-effective option because of limited healthcare accessibility.
Although health professionals often utilize behavior change techniques (BCTs)
to boost physical activity levels and enhance client engagement and motivation
by affiliative humor, the efficacy of humor in chatbot-delivered interventions
is not well-understood. This study conducted a randomized controlled trial to
examine the impact of the generative humorous communication style in a 10-day
chatbot-delivered intervention for physical activity. It further investigated
if user engagement and motivation act as mediators between the communication
style and changes in physical activity levels. 66 participants engaged with the
chatbots across three groups (humorous, non-humorous, and no-intervention) and
responded to daily ecological momentary assessment questionnaires assessing
engagement, motivation, and physical activity levels. Multilevel time series
analyses revealed that an affiliative humorous communication style positively
impacted physical activity levels over time, with user engagement acting as a
mediator in this relationship, whereas motivation did not. These findings
clarify the role of humorous communication style in chatbot-delivered physical
activity interventions, offering valuable insights for future development of
intelligent conversational agents incorporating humor.
