Fifty years ago, most people's daily levels of activity were equivalent to walking three to five miles a day; today, the average person fails to cover that distance in a week.

It's no wonder the incidence of obesity has soared - with serious implications for health.

The culprit? Inertia. What we have gained in convenience from labour-saving devices over the past half-century, we have paid for in terms of a sharp decline in physical activity.

We use cars, buses or trains to get to work; our children are driven to school; escalators and lifts have replaced conventional stairs in shopping centres, offices and apartment blocks.

Washing machines, vacuum cleaners, dishwashers and electric mowers all minimise the effort required to maintain a clean and tidy home.

Television has us tethered to the sofa.

Almost one third of adults spend over ten hours sitting down every day, adding up to a staggering average of 32 years and four months over a lifetime.

Hardly surprising, then, that researchers blame this sedentary lifestyle for our weight gain.

Of course, our diets have changed, too, but the fact is we consume fewer calories now than in the 1960s.

Our waistlines are expanding for one major reason: increasing inactivity.

So what is the solution?

The secret is integrated exercise. This involves going about your normal daily life - but doing it with moregusto.

It might mean standing to answer the phone and pacing the room, tapping your feet on the floor as you work.

It means never taking the car when you could walk; it means standing on short train and bus journeys, or walking at a pace where you feel you might break into a run if you were to go any faster.

A Dutch study found that people who spend more time doing moderate, integrated-style exercise burned more calories than those who performed shorter, sharper workouts.