There is little evidence supporting the claim that mass participation sporting events (MPSE) increase the population's physical activity (PA). This research aimed to identify the demographic, motivational and PA profile of participants in a women-only non-elite triathlon race series. It also aimed to identify whether PA in previously insufficiently active participants increased before the event, and remained elevated three months after the event. Participants were surveyed before (n=452) and three months after their event (n=95). The results showed that the participants were predominantly sufficiently active prior to the event. Although PA levels decreased post-event, they remained predominantly sufficient. Nearly 50% of the inactive women pre-event remained sufficiently active three months after their event. Challenge and competition were key motivators for participation. MPSEs facilitate previously inactive women into sufficient levels of PA. Further research should explore their capacity to facilitate long-term maintenance of PA.