Before you start

This is a short book and you can read it in two or three sittings. I notice the irony of that word. If you like, read some of it standing up.

It's about one habit, though most people who have it wouldn't call it a habit. You sit in the car, then at a desk, then at a table, then on the sofa. Nobody decided this. It's how work, travel and evenings are arranged. Somewhere in your forties or fifties you start to feel stiff when you stand up and flat by mid-afternoon, and you put both down to your age.

I'm going to argue three things. The first is that a good share of what you're calling age is the effect of not moving, which is a different thing and behaves differently. Age only runs one way. The effects of not moving can be reversed, and there's evidence for that in people of fifty and in people of ninety. The second is that the usual answer, which is to join a gym, misses the point for most people. An hour of exercise is good for you, but it doesn't reach into the other twelve hours of sitting unless it's a lot of exercise. The third is practical. You get up every half hour, and you walk for ten minutes a day. Chapters 13 to 15 cover how, and what to do when your job or your body makes that awkward.

Nothing in this book asks you to stop sitting. Sitting is a fine thing to do. You can't do most jobs, eat a meal or watch a film without it. The argument is about long unbroken stretches and about days with almost nothing else in them.

Four cautions.

If you haven't been active for some time, or you have a medical condition or any concerns, the NHS advice is to speak to a GP before you start exercising. Nothing in this book is strenuous, but that advice still applies to you, and a GP can tell you what suits your heart, your joints and your medicines.

If you've been tired for a few weeks and you're not sure why, or tiredness is affecting your daily life, the NHS advice is to see a GP. The same goes if you're tired and you've also lost weight, your mood has changed, or you've been told you gasp, snort or choke in your sleep. Tiredness has many causes. This book deals with one of them, and I'd like you to have the others ruled out.

If you get chest pain, stop what you're doing. The NHS says to call 999 if you have sudden chest pain or discomfort that doesn't go away, pain that spreads to your arm, neck, jaw, stomach or back, or chest pain with sweating, sickness, light-headedness or shortness of breath.

And if you have ME, also called chronic fatigue syndrome, or you're living with long Covid, most of this book doesn't apply to you. Your tiredness isn't the kind I'm describing, and pushing through it can make you worse. Chapter 15 says a little more. The same chapter has a section for readers who use a wheelchair or can't stand.

The notes at the back give my sources and their limits. Where I'm giving my own reasoning and not a finding, I'll say so.