April 6th was World Physical Activity Day—did you miss it? Probably good news. Best to keep doctors out of it. Let me explain: I believe passionately in the benefits of physical activity, have researched it, published, editorialised, practised, and promoted it at every opportunity. The benefits of physical activity are undisputed and physical activity is to be encouraged, supported and facilitated where ever possible. But I am not sure that doctors have a central role.

Let me put my hands up. I used to think general practitioners had a key role in encouraging patients to be active and, early in my career, wrote passionately about promoting physical activity in primary care. Indeed, as one of the pioneers I was pivotal in our regional exercise prescription scheme. But, sadly, the evidence supporting physical activity promotion through general practice is weak—including two recent UK meta-analyses published in the BMJ. I changed my mind. And, on the basis of published evidence, I’ve had a 180 degree reversal in my original opinion. That doesn’t mean exercise is ineffective or that doctors should not support it—it just means that GPs are not major agents in passing on the message or in changing people’s behaviour.

How can we promote physical activity? It’s about the environment, the culture, the acceptability of exercise. We need to change the way we think: to redesign cities to achieve mass cycling participation like Amsterdam and Copenhagen, or to think as a country, like Norway where a whole nation embraces its national sport—cross country skiing (and where there are street lamps in the forest so people can ski on winter evenings) or Brazil where there are outdoor fitness centres in parks, community spaces and even beside health centres. And at local level, is it safe enough to cycle on the road, is there somewhere to park your bike, adequate street lights, segregated bicycle lanes? Are there showers in your workplace, is it easier to take the lift or the stairs, could you go for a run at lunchtime. Is there a crèche at the gym, exercise modalities available for every age? Is there somewhere you can jog safely, is the car park secure at the leisure centre, is your children’s sport supervised?

Don’t let politicians pass the ball to doctors. Inactivity may cause health problems but that doesn’t mean there is a health solution. If there is a health component, it is in public health advocacy (see the NHS Choices “Couch to 5k”—it’s superb). We cannot allow government to make exercise a health issue—that’s too easy. It allows them to shed their responsibility rather than change policy, work across departments, or introduce legislation to change the environment, the workplace and improve leisure accessibility.

It’s all about facilitating community action, social movements, tipping points. It’s not just writing a prescription.

Domhnall MacAuley is primary care editor, BMJ.