25% of Brits do fewer than 30 minutes activity a week

The second pillar of the global obesity pandemic, and a major risk factor for many of the world’s other most deadly diseases, are rising levels of physical inactivity. To illustrate how widespread the problem is, Chris Smith spoke to Cambridge University epidemiologist, Soren Brage…

Soren - If we look at UK surveys, about two thirds of the population are meeting the recommendations of 150 minutes of moderate to vigorous activity a week and a quarter of the population do less than half an hour of activity a week. So that's quite alarming.

Chris - It is alarming, isn't it? What do we mean by activity, though?

Soren - That's a good question. So, obviously our metabolism is mostly made of our resting metabolic rate and activity is the energy expenditure that sits on top of that. And it really is everything we do above that of rest. So even if you move your little finger, technically that is activity, but obviously we'd like people to use their large muscle groups.

Chris - How do we actually get these sorts of numbers, though, to work out that a certain fraction of the population are getting about the right amount of activity and a certain fraction are not? Is that self-reported and is it therefore subject to the same risks of bias where, if you ask people how much they eat, you can get misleading answers?

Soren - It certainly is. So the UK has national surveys where we ask people about their various activities and it's only a fraction of the activities people actually do over the day that you can ask about in a survey like that. Then, we add it all up. If you get to 150 minutes a week, we say you meet the health recommendations. If you get to double that, we say you meet the upper health recommendations for physical activity. But of course that is prone to bias. If we measured things with devices, we would get very different answers, but also very different health associations.

Chris - Is a stroll around the block as good as a jog? Can you actually make that sort of comparison? Or is any activity better than no activity, but the more intense the activity, the better

Soren - Intensity does matter. But really it is important for most people to just think about the totality and worry less about the nuances of intensity. They can do that if they have the luxury of being at a nice high total activity level.

Chris - And if we compare today with, say, 50 years ago, is there a difference?

Soren - So the data is a little bit uncertain on that but if we, for example, look at the makeup of our jobs, we had many more manual jobs in the past. We now have more service oriented types of jobs and desk oriented jobs. So yes, certainly that big proportion of many people's lives would have changed and, accordingly, people's activity levels would also have changed.

Chris - In the nearer term, though, what effect did the pandemic have?

Soren - That data is a little bit more certain because we have standardised surveys that cover this. The Active Life Survey, for example, that Sport England runs, we could see that there was a steady trend and then the pandemic really hit us quite hard because people's opportunities for being active and going to work, either walking or cycling, were taken away from us. So 2020 was not a great year. Levels do seem to have more or less recovered, though, so the latest data do suggest that we're more or less back to where we were except perhaps for one thing: active travel to and from work has not fully recovered yet. That is probably a reflection of our work and whether we work more days from home will obviously mean fewer active journeys for those who would otherwise have walked or cycled to work. So, at a population level, that number has not quite recovered yet.

Chris - In summary, then, you are saying that activity levels now are lower than they have been in the past. Is that just down to doing a job that makes us active or are people just lazier? Why would this have happened otherwise?

Soren - It probably isn't all down to personal level factors. There are many other things in our society. It is perhaps also the way that we have constructed our cities; maybe they're not always so welcoming in terms of being active. If you are afraid you might be run over by a bus or a truck cycling into work, then you are less likely to do that. It is really a 360 sort of approach we need to use when thinking about how we might build a better society and a better infrastructure so that we support people in making the right decisions for their own health.