"I'm not the exercising type"

Other readers will have the opposite worry. You don't swim or go to classes. You may have joined a gym twice and stopped going both times. If the people who exercise aren't fully covered, you might reasonably wonder what hope there is for you. And if the answer to sitting is an hour a day of brisk walking, you know already that you aren't going to do it.

This chapter has the most encouraging evidence in the book. It turns out that the largest gains are at the bottom of the scale.

The studies in the last chapter relied on people's own reports. Newer studies give people a motion sensor to wear for a week, which records every minute of movement, including movement nobody would think to call exercise. Ulf Ekelund and colleagues pooled eight such studies covering more than 36,000 adults with an average age of about sixty-three. They divided people into four equal groups by total movement and followed them for around six years.

Compared with the least active quarter, the next quarter up had about half the death rate over the follow-up. The steps after that gave further gains, but smaller ones. Most of the difference lay between people who barely moved and people who moved a bit.

The researchers also looked at light activity on its own. That's the kind that doesn't raise your pulse much, such as walking slowly, cooking, pottering, tidying and standing at a counter. The same pattern held. People who did more of it had lower death rates, and the second quarter had about 40 per cent lower rates than the bottom one. For time spent sedentary, the pattern ran the other way, and the most sedentary quarter had more than two and a half times the death rate of the least.

The caution from the last chapter applies here with more force. People who are already ill move less, and they're also more likely to die, so some of this gap reflects illness causing stillness and not the reverse. The researchers took steps to reduce that problem, and I doubt it can be removed completely. The size of the differences is probably flattered by it. The direction is supported by the experiments in the next chapter, where the movement is assigned and the effect on the body is measured the same day.

Step counts tell the same story in a form you can check on your phone. Amanda Paluch and colleagues pooled fifteen studies covering about 47,000 adults. They note at the outset that there's little evidence behind the famous target of ten thousand steps. In their data the quarter of people who walked least took about 3,500 steps a day. The next quarter took about 5,800 and had a death rate 40 per cent lower. Beyond that the gains went on but flattened out, at around six to eight thousand steps a day for people over sixty, and eight to ten thousand for younger adults. For someone with a thirteen-hour tally, the useful distance is from three and a half thousand to six thousand. That's about twenty-five minutes of walking spread across a day.

One more finding speaks directly to people who don't exercise. Emmanuel Stamatakis and colleagues studied more than 25,000 adults who wore sensors and who reported doing no sport or exercise at all. Some of them nonetheless showed short bursts of vigorous effort in the course of ordinary life. They climbed stairs fast, hurried for a bus or carried heavy shopping. Those who managed three such bursts a day, each lasting a minute or two, had a death rate 38 to 40 per cent lower over seven years than those who had none. It's observational again, with the same caveats. But none of these people would have described themselves as the exercising type, and their sensors agreed.

The belief this chapter examines rests on an assumption, which is that the alternative to sitting is exercise. For your body, the alternative to sitting is anything else. Standing at the worktop peeling potatoes counts as light activity. So does walking to a colleague's desk when you could have sent a message, and so does carrying the washing upstairs in two trips. The NHS list of what counts as light activity for older adults includes getting up to make a cup of tea.

You don't have to become someone who exercises in order to stop being someone who sits for thirteen hours. Those are separate projects. The second one needs no kit, no membership and no change of clothes, and on the evidence it's where the larger gains are.