Sitting in front of a computer all day can rob you of fitness, health and even your life. A recent study that found men between the age of 25 and 34 scored lower on cardio-respiratory fitness tests than those aged 35 and 39 has underlined what doctors, fitness and sports medicine researchers have long suspected. Forced inactivity is destroying people's health. Between the ages of 25 and 30, a man is supposed to be at the peak of his physical powers. He's over the energy-sapping growth of adolescence; has filled out as his muscles have grown to build on his fully formed bones; and his heart, lungs and blood circulation have adjusted to his fully matured body. His brain is also better able to control his muscles, bones and joints. A University of Hong Kong study carried out in the mid-1990s on teenagers found that they had excellent aerobic fitness levels - some of the best in the world - but were already showing poor endurance. The researchers concluded that this meant the teenagers were genetically excellent, but that the Hong Kong lifestyle - which can leave little time for exercise - meant this was being wasted. Worse - it was being actively destroyed. Those teenagers are now young adults - about 25 to 30 year olds - and are showing poor aerobic fitness levels. We've known for at least 10 years that lack of exercise can harm young people's health, but we've done nothing to change it. Not that Hong Kong is the only place with such a problem. In the US, health economists have calculated that lack of exercise and poor diet costs US$33 billion a year in medical bills, and US$9 billion in lost productivity caused by heart disease, cancer, stroke and diabetes. In 2000, health-care costs associated with physical inactivity were estimated at more than US$76 billion. US researchers have also calculated the benefits of spending money to increase exercise levels. They found that, if 10 per cent of adults began a regular walking programme, US$5.6 billion in heart disease costs could be saved. They also found that exercise could prevent the financial and social costs of hip fractures, calculating that every US$1 spent on physical activity programmes for elderly people with hip fractures resulted in a US$4.50 return. In Hong Kong, it's been estimated that 6,400 deaths a year are caused by lack of physical activity. The case for getting out of that chair and on to the street, into the swimming pool or on to the football field is a strong one. But who has the time? The physical activity levels now recommended are an hour of moderate to intense activity every day. These have been increased from 30- 60 minutes three times a week recommended during the 1990s. In other words, we need to be doing a lot more than we thought. And yet we're probably doing less than ever. Unless you're retired or married to someone wealthy, it's hard to schedule this level of exercise every day. So, what about a more realistic approach? In Australia, the National Heart Foundation recommends you take 10,000 steps every day (you can measure this with a pedometer) to reach a physical activity baseline. Pedometers are relatively cheap and easy to find. And, if you sign up for the MTR's Hong Kong Race Walking 2005 in April, you'll get one for free. Application forms are available from some MTR stations and from the Hong Kong Amateur Athletic Association's website at www.hkaaa.com . Inquiries: 2504 8215. The entry deadline is March 11 ... so get off that sofa.