I don't normally like meta-analysis because it is so difficult to get a feel for the individual studies - I worry about garbage in garbage out even if the analysts have applied quality scores. But Today I make an exception: I need to see the wood for the trees. There have been many small studies which tried to get people to exercise more.
Enough metaphors for now. Here is the meta-analysis.Over 350 studies were included (like I say, there have been a lot of them); the authors paid particular attention to heterogeneity i.e. the studies and their results were all different. One key to this is use of the "random effects" model.
Difficult to summarise all those studies but looking at the first and third quartiles of the studies, most were aimed at middle aged women (40 - 50 years old), and consisted of one-hour group sessions, with between 16 and 48 sessions. Overall the answer seems to be that you can increase physical activity, by about 500 extra steps per day - I guess we'd call this modest but useful.
Various other points of interest - using fancy models such as social cognitive theory or the transtheoretical model seemed to make things worse; goal setting, rewards and other behaivoural strategies made things better. The actual amount of exercise during the programme seemed irrelevant:
"Neither the number of intervention strategies
nor the total minutes of intervention content
(including total minutes of supervised physical
activity) was associated with physical activity
This may fit with the theory that self-identity is important to behvaiour change: if you start to think of yourself as 'an exerciser' you will take more exercise; so perhaps participating in a programme achieves that switch in self identity?