Why don't stage-based activity promotion interventions work?

Despite the well-described benefits of regular physical activity, around 70% of adults in the UK fail to meet current activity recommendations. Interventions based on the Transtheoretical, or Stages of Change, Model of behaviour change have been proposed as one potentially effective method of promoting physical activity levels. However, two recent reviews have found little evidence that individualized stage-based activity promotion interventions are any more effective than control conditions in promoting long-term adherence to increased levels of physical activity. Possible reasons for this are: that exercise behaviour is a more complex group of behaviours than currently recognized; that many algorithms for determining current stage of activity change have not been validated; that exercise behaviour is determined by a number of factors not addressed by stage-based interventions; that the stages of change model encourages focus on stage progression which is not always associated with behaviour change; and that truly stage-based interventions are highly complex requiring more than one level of development and evaluation--a challenge that has not yet been met. Thus, stage-based activity promotion interventions may simplify exercise behaviour beyond what is useful for practitioners and health promoters. Paradoxically, stage-based activity promotion interventions that have been developed to date may have failed to appreciate the true complexity of the task.