27 May 2010
You may hit the gym at lunchtime or go for a run when you get home. But such efforts will have minimal effect if you spend the rest of your time doing what you are probably doing now - sitting down.
In a glut of new research on the subject, experts are warning that we should 'beware our chair', as spending too long in it can raise the risk of high blood pressure, a sluggish metabolism and weight gain.
With the average person sitting down for just under nine hours a day at the office, at home or in the car, even a daily workout is unlikely to offset the risks of being seated for too long.
According to Swedish scientists, quoted in the British Journal of Sports Medicine recently, prolonged sitting should carry a public health warning.
So why is the humble chair being blacklisted? As the most passive activity behind lying down, being seated burns a bare minimum of calories - even eating an apple or fidgeting uses more energy than parking your bottom on a chair.
While standing engages muscles in your back, shoulders and legs, sitting presents no positive physical challenge to the body, forcing it instead into an inactive state.
It is almost inevitable, researchers say, that long-term sitters find their waistline expanding.
While the action of standing up only burns a few calories, do it enough times a day and it makes a real difference.
It's easy to burn 30 to 50 extra calories a day, which is enough to prevent a weight gain of 2lb to 3lb a year. Spend your time sitting down and the pounds will creep on unnoticed.
On average, thin people stand for two hours longer every day than those who pile on the pounds.
The Swedish researchers found that the desk-bound and couch potatoes are much more likely to suffer weight-related health problems than those who move about regularly, even if it's just to get up to make a coffee.
'Prolonged sitting really isn't good and yet a lot of people think they are more active than they actually are,' says Stuart Biddle, a professor in exercise psychology at Loughborough University, who is speaking on the adverse effects of 'the seated generation' at an international conference in August.
'People mistake the term for "sedentary" for meaning "no exercise", but if someone goes to the gym or walks for 30 to 45 minutes a day, but sits down the rest of the time, then they are still described as having a "sedentary lifestyle".'
It's not just weight gain that makes sitting down the latest health worry. Emerging research suggests something more sinister happens when we are inactive for too long at a time.
Studies on rats have shown that substances that are produced only when muscles are being used play a crucial role in metabolising fat and sugar.
These substances can be made just by standing up or moving around. When you sit down, an important part of your metabolism slows down.
'This can eventually lead to disorders like diabetes,' says Biddle. 'But the important thing to realise is that people who get up every half an hour or so are much less likely to have these effects.'
Regular movement is also important for preserving good posture. Sammy Margo, spokesperson for the Chartered Society of Physiotherapists, says that the human spine wasn't designed to spend long hours seated and that doing so can play havoc with posture, breathing and digestion.
A healthy human spine has a natural S-shape, but sitting pushes the lower lumbar curve into more of a C-shape so that the back and abdominal muscles designed to support the body are unused.
Over time, the postural muscles become so weak that they are unable to support the spine effectively and back pain inevitably ensues.
'With your knees at a 90-degree angle when you sit, your hamstring muscles and hip flexors are permanently shortened and your buttock muscles stretched,' says Margo.
'This leads to muscles and joints tightening so much that your body moves less freely and is more prone to pain and injury.'
Breathing is also hampered, Margo says, as the body struggles to fill the lungs with oxygen when crunched in a seated position. Sitting also crunches the abdominal contents and digestion is slowed down as a result.
'All of this means energy levels can flag through lack of oxygen and sluggish digestion,' says Margo. 'Because your abdominal muscles are not being engaged when you sit, you will also lose tone in that area.
'It's not good news and my advice is to stretch or go for a short walk as often as you can.'
There are other options for the permanently seated. Chairobics, or deskercise movements that can be performed discreetly as you sit, will prevent your muscles from remaining dormant.
Meanwhile, the next big thing could be the office treadmill - already available in the U.S. - on which you walk as you work. But the next best thing is simply to stand up more often.
'Get into the habit of standing up when you are on the phone,' says Biddle. 'Naturally your body shifts its weight from foot to foot when you stand. You'll be burning calories as you talk.'