A growing body of evidence for the associations between active travel and reduced risk of cardiovascular mortality, overweight and obesity, hypertension and type 2 diabetes, supports its promotion as a way of improving public health . These health benefits are likely due, in large part, to the extent to which active travel results in greater total physical activity.
The findings of a recent review  and of other studies [3–7] suggest, fairly convincingly, that in adults active travel is associated with greater self-reported total physical activity [8–10] accelerometer-determined total physical activity [3, 5, 11] and total step counts [4, 7]. Furthermore, studies that have examined associations between active travel and recreational physical activity in particular suggest that active travel is not necessarily undertaken as a substitute for recreational physical activity [12, 13]. In some studies active travel was associated with greater time spent in recreational physical activity [11, 14–16]. For example, adults in one study who travelled mainly on foot or by bike reported a statistically significant additional 15 min/day in recreational physical activity compared with adults who never or rarely travelled by bike or on foot .
Although encouraging, previous research has been limited by the use of crude measures of active travel (i.e. usual travel mode) and the investigation of only one travel purpose or mode (i.e. commuting). A UK study recently extended this work by simultaneously collecting more detailed information on travel and recreational physical activity. Findings indicated that active travel was done in addition to, rather than instead of, recreational physical activity and suggested a dose–response relationship between active travel and total physical activity .
Nevertheless, there is currently little evidence that an increase in active travel results in a commensurate increase in total physical activity. It is possible that an increase in active travel might be compensated for by a decrease in activity in other domains. For example, a person may start walking to work and subsequently forego their morning recreational walk. Alternatively, as has been suggested in studies with children, an increase in active travel may result in greater total physical activity, either because recreational physical activity remains unchanged  or because active travel encourages physical activity in other domains .
In adults, it is important to establish the association between a change in active travel and change in total physical activity to strengthen our understanding of the population health impact of promoting active travel. This paper therefore builds on previous cross-sectional research in the UK population-based iConnect study  by examining the longitudinal association between a change in active travel and changes in recreational and total physical activity.