Nanette Mutrie of Glasgow University has a message for the couch potatoes whose New Year resolution is to get fit after the excesses of the festive season: take it easy.

Dr Mutrie, senior lecturer in biomedical and life sciences, has been researching the perceived barriers to becoming fitter, and how these can be overcome.

"January is a time when people's motivation to change their behaviour is very high," she says. "The main thing that people saw as a barrier to becoming more active was time. The old message was that you needed to do at least 20 minutes of continuous activity, but the new message is that some activity is better than none, and you can accumulate small amounts over a day."

The goal should be to accumulate 30 minutes' activity on most days, which can include using stairs rather than lifts, parking or getting off the bus further away from your destination, and doing some gardening when the weather allows.

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"The second barrier is that people find it takes too much effort. They get sore or tired, and put themselves off before they're started. You have to aim for a gradual change from a relatively inactive life to a more active one."

Taking a whole aerobics class as your first New Year exercise is a bad idea, Dr Mutrie warns. Try walking more frequently, and attending half a class, with the goal of completing a whole class after six to eight weeks.

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Another barrier is lack of support, and Dr Mutrie suggests exercising with friends, family or in a class to boost motivation. Most higher education institutions have a sports service which will advise on classes or opportunities to exercise.

The Glasgow researchers are trying to promote "active commuting", using walking or cycling as a convenient form of exercise. But it remains to be seen how they propose overcoming the barriers of winter darkness and miserable weather.