Sitting all day: the gym doesn't cancel it out.

Breakfast sitting down, then forty minutes in the car. The desk, two meetings, lunch at your desk, more meetings, the drive home. Then the sofa. Add it up: ten hours in a chair, maybe more.

On average we sit more than nine hours a day, about as long as we spend in bed. I see it often in the business owners and managers I work with, even those who train regularly. And few people expect this: training alone doesn't make up for the chair.

How you can tell

Your body tells you by evening, with signs most of us put down to age.

• Your back complains when you stand up. After a long meeting, you take your first steps bent forward.
• Swollen ankles in the evening. Your socks leave a mark and your legs feel heavy.
• Rounded shoulders, head forward. You notice it in photos, or in a stiff neck on Friday.
• Shallow breathing. You breathe high in your chest and sigh a lot.

What a chair does to your body

Sitting, you move less than you do chewing gum. Your body takes that literally and shuts things down one by one.

Your legs stop pumping. When you stand, over half the blood in your veins is in your legs, and it needs your calf to get back to your heart. With every step the muscle squeezes the veins like a sponge. Stay still and the pump stops, so fluid pools lower down.

Your hips tighten. The psoas, the muscle joining your spine to your thigh, stays folded for hours. When you get up it struggles to lengthen and pulls on your lower back. That's why those first few steps hurt.

Your chest closes. Hunched over a screen, your diaphragm has less room, and your breathing turns short and high.

The gym doesn't settle the bill. Train three times a week and sit the rest of the day, and there's a name for you: an active couch potato. Movement spread through the day (walking, stairs, standing) can reach a fifth of the energy you burn. Training usually accounts for less.

How to break up the sitting

Two minutes on your feet, every hour. That's the minimum. If your day allows, every half hour. The more often, the better. Set a phone reminder and walk to the window. Your calves get going and your hips open up. Deep in something? Read on standing up. And take screen-free calls walking. It costs you no time.

Fifteen chair stands. For when you can't leave the room. Stand up and sit back down fifteen times, no hands. Thighs and glutes are the muscles the chair squashes and starves of oxygen. This gets them going again.

Three office moves. Rise onto your toes and lower slowly, holding the desk: that's the calf pump. Hands behind your head, elbows wide, open your chest and take a few deep belly breaths. Then a long step back, hips forward, until you feel a pull at the front of the hip. Go gently. The psoas has to be coaxed.

Ten minutes' walk after lunch. Working muscles take up the sugar from your meal, and the afternoon starts lighter.

Seven to eight thousand steps a day. The benefit for how long you live keeps rising up to there. Beyond that, gains are smaller. Park further away, take the stairs, get off a stop early.

Strength training is still the foundation, and deserves its own article. For now, set the first reminder. In an hour it goes off, you stand up, and it's already a different day.