It takes me 15 minutes to cycle to and from work each day. I read recently that you need to exercise for more than 20 minutes at a time for it to make any impact on fitness. So are my bike rides contributing to improving my fitness?
Gregory Holmes, Catterick

Matt Hart, personal trainer replies:
Any exercise you do will have a positive impact on your fitness levels so don't be put off. If you're cycling 15 minutes each way, that's 30 minutes a day or 2 hours a week.

To get the most out of it, vary the intensity of your rides so you push your body harder every other day. Use the first five minutes of your ride to warm up and then on your ‘hard’ days do one of the following routines for ten minutes:

1. Select a high gear and stay in it all the way, even if you have to stop at traffic lights.
2. Choose a landmark to sprint to, increasing your effort, then ease up and spin gently when you get there. Then choose another landmark, repeat and so on all the way to work. This is called fartlek training.