It seems like a good idea at the time. Full of goodwill on New Year's Day, you decide this is the year you are going to shed weight and get yourself into trim.

A couple of days later, as the alarm goes off in the morning and it's pitch black and raining outside, all those good intentions fall by the wayside.

But health experts say if you can manage to make the effort, it will all be worth it in the long run.

If early-morning jogs are not for you, even making the decision to walk more often can do a lot of good.

Health bosses say walking to the train station for work each morning or making your way to the shops on foot instead of by bus can make a lot of difference if done regularly. Signing up with a gym can also help, along with swimming or other sports.

With cars on most driveways and the decline in the number of physically active jobs, 70 per cent of adults are inactive enough to be classed as sedentary, which increases the risk of a heart attack or stroke.

Despite the strong case for staying active, many people find it difficult to adapt their daily lives to incorporate physical activity.

Many people are put off because they believe only vigorous exercise or playing sport counts as healthy activity.

But, in fact, substantial health benefits can be achieved from regular activity without the need for special equipment, sporting ability or getting very hot and sweaty.

There is now strong scientific evidence that moderate-intensity physical activity - equivalent to brisk walking for 30 minutes per day on most days of the week - is enough to bring about real benefits in terms of promoting health and preventing illnesses.

Regular activity can also improve the way you look and feel. In combination with a balanced diet, regular activity can help to maintain a healthy weight, boost self-confidence and reduce the risk of depression.

For an adult, regular, moderate-intensity physical activity means using up an extra 200 calories per day, most days of the week.

This equates to about 30 minutes of activity, such as a two-mile brisk walk, which should make you feel warm and mildly out of breath. You should still be able to talk without panting in between your words.

If you have previously been inactive and 30 minutes of activity per day sounds like a tall order, the good news is separate sessions of ten minutes can count towards the total.

It's possible to achieve your 30-minute target by making fairly simple changes to your everyday routine, without joining the gym or running a marathon.

Everyday activities that count can include walking up stairs instead of using lifts, walking up moving escalators, walking instead of driving for short journeys, doing the housework at "double-speed", DIY and gardening, such as painting or raking leaves.

The ability to keep up a physical activity such as jogging, racket sports, cycling or swimming is related to your aerobic fitness - or stamina.

Generally speaking, the greater your stamina, the greater the health benefits. If you want to improve your stamina, it's important to start gently, increasing the frequency of your activity before increasing how hard you exercise.

The key to keeping up with a resolution to get fit is finding an activity, or range of activities, that you enjoy.

Not everyone sees exercise as fun and doing something you find boring just because it's good for you is very difficult to sustain. But you can take steps to make it more enjoyable.

Try out new sports or activities until you find something you like. Once you've found an activity you enjoy, try exercising with a friend at a pace which still allows you to talk.

Try exercising in beautiful scenery, such as on a beach or in a park. Maybe you could buy yourself some new exercise clothes that you like wearing and feel good in.

Even when you usually enjoy exercising, there will be days when you just can't seem to find the motivation to get active.

Practical tips to help maintain enthusiasm include keeping a diary and setting short and long-term goals.

A spokesman for the healthcare company Bupa said: "Exercising releases chemicals in the brain, such as serotonin, which have a strong effect on your mood, helping reduce anxiety, stress and depression.

"So whenever you don't feel like exercising, try to remind yourself how good you'll feel afterwards."