Testing motivational and self-regulatory mechanisms of action on device-measured physical activity in the context of a weight loss maintenance digital intervention: A secondary analysis of the NoHoW trial

•The logic model based on theories of behaviour change yielded poor fit to the data.•Simpler logic models were tested and presented a better fit to the data.•The theoretical relationships between the psychological mechanisms were confirmed.•However, explained variance of device-measured physical activity was negligible.•Models of behavior change may need refinement to explain long-term physical activity among weight-loss maintainers.