"Stiff means worn out"

The noise you make when you stand up comes with a picture. In the picture, your joints are mechanical parts that have done a lot of miles. The stiffness is wear, like a hinge that's gone rusty, and the kind thing to do with a worn part is to use it less.

Test the picture against what happens at the front door. You stood up stiff. Three steps later you were less stiff. By the time you'd carried the parcel to the hall table you were moving normally. A worn hinge doesn't free up after three swings. Whatever eased in those few seconds wasn't damage, because damage doesn't ease by being used.

What you felt is better described as the state of a body that's been held in one shape for two hours. I'm simplifying, and the details differ from joint to joint, but the outline is well accepted. Muscles held short for a long time, such as the ones across the front of your hips when you sit, resist being lengthened in a hurry. Joints are lubricated by movement, and a joint that hasn't moved for a while is briefly less ready to. Tissues that have been sat on have been squeezed. All of this reverses within a minute or so of moving, which is what happened.

Notice when the stiffness is at its worst. It peaks first thing in the morning, after a long drive, and at the end of a film. It's at its lowest halfway through a day of pottering about. If stiffness tracked use, it would be worst after use. Yours is worst after stillness. The pattern points to stillness as the cause.

The wear picture does more than mislead you. It tells you to protect your joints by resting them, which means more stillness. That brings more stiffness, which you take as more evidence of wear. People can go round that loop for years.

There's a fair objection here. Some stiffness is more than the ordinary kind, because arthritis exists. Osteoarthritis is common from middle age on, and it's a real change in the joint. But look at what the NHS says to people who have it. It calls exercise one of the most important treatments for osteoarthritis, whatever your age or level of fitness. It acknowledges that if your joints are painful and stiff you may think exercise will make things worse, and says that regular exercise that keeps you active and builds up muscle usually helps to improve symptoms. So even where there's genuine wear in the joint, the medical advice is to move it.

I also owe you a correction to something you may have read, because it's the kind of claim a book like this would be tempted to make. It's often said that sitting at a desk wrecks your back. Darren Roffey and colleagues reviewed the research on whether sitting at work causes low back pain, and found strong and consistent evidence of no association. They concluded that occupational sitting is unlikely to be an independent cause of low back pain. So I won't tell you that your chair has injured your spine, because the best evidence says it probably hasn't. What I'm describing is milder and more general. Your body has adapted to being still and objects for a moment when asked to move. That isn't an injury.

I find that reassuring, and I hope you do. The grunt, the three odd steps and the hand on the coffee table tell you that you've been still for a long time. They don't tell you that your joints are failing.

Some kinds of stiffness and pain do need a doctor, and I'd like you to know which. The NHS advises seeing a GP about back pain that doesn't improve after a few weeks, that stops you doing your day-to-day activities, or that's worse at night. It advises urgent help if back pain comes with numbness or tingling around your genitals or bottom, loss of bladder or bowel control, or weakness or numbness in both legs. Joints that are swollen, hot or red are also worth taking to a GP, and so is morning stiffness that lasts much longer than half an hour. Ordinary sitting stiffness doesn't do these things. It eases within a minute or two of moving about.