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About 30% of Britons never exercise, according to research by Mintel. But what can people do to get slightly fitter without incurring costs, inconvenience or embarrassment, asks Lucy Townsend.

1. Jog up and down the stairs five times. Exercise doesn't have to take an hour, short quick bursts of activity can be beneficial. Fitness guru Rosemary Conley suggests jogging up and down the stairs at home. "It's free, it's easy, it doesn't take very long and it gets you out of breath," she says.

2. Do the plank. Face to the floor, arms locked in an L-shape, legs straight and bottom firmly in line with the rest of your body and not under any circumstances sticking up into the air. The plank, loathed by many, is the best exercise for improving core strength, according to Elliot Lake, general manager of Bootcamp Pilates. "Aim for 30 seconds, three times a week and that would be a huge help," he says. The core comprises all the deep muscles that connect the upper and lower body, including stomach, back, hips and buttocks. Benefits include a flatter stomach and a better posture, as well as strength around the spine. "The idea is that you work up to a minute three times a week," Lake adds.

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3. Start hoovering more. "It's really hard work and you can get quite a sweat on," says Conley, who runs a daily 20:00 GMT fitness session from her Twitter account. "Washing the car is also a good one, as is gardening and mowing the lawn." The benefit, Conley says, is that these are activities that will raise the heart rate - the NHS advocates at least 150 minutes of moderate-intensity aerobic activity every week.

4. Write the alphabet with your leg. Another of Conley's methods. "Sit on the front half of the sofa, lift one leg and draw the alphabet in the air with your toe, then do it with the other leg," she says. "It's easy to do while you're sat down watching television."

5. Set an alarm. "A regular reminder to stand up or walk can be helpful," says Dr Lauren Sherar, senior lecturer in physical activity and public health at Loughborough University. "Put a reminder in your phone to regularly get up and stand for five minutes. Or go for a five-minute walk." Doctors have warned that sitting down for too long can shorten lives, and regularly standing can improve health. "Standing for five minutes every 30 minutes is an achievable goal," adds Sherar.

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