I have an exercise bike in the corner of my office. The theory behind this is that I can hop on to it, pedal furiously (30 mph is good), for 30 seconds four times a day, and this is sufficient to keep my heart healthy, improve my brain, and boost my learning ability, as well as reverse signs of ageing.

I am constantly amazed at how difficult I find it to spare this small amount of time, after all I can see it out of the corner of my eye. So why is it such a chore. While I was starting to write this article and waiting for inspiration, I hopped on and did 30 seconds worth and was very pleased to find that I was out of breath, after all it is the aerobic benefit that is good for you.

I have no problem at all sitting down at lunchtime with the daily paper and completing one or two Sudoku puzzles; and I thought that this was doing me good; but I read an article the other day that contradicts this thinking, by stating categorically that exercise is the most beneficial natural thing that you can do to stay mentally alert.

A few years ago I bought a pedometer, as I had read another article which said that everyone should aim for 10,000 steps a day. At the time I was not spending most of the day sitting at the computer, and I found it easy to do my 10,000 steps, especially in the summer months when a good walk with the dog could add up to 5,000 to 7,000 steps. Also at that time we lived in a house with stairs, and my office was upstairs, so I used to get a lot of my daily exercise running up and down stairs.

Now, however, we live in a ground floor flat, the dog is nearly 13 and she does not want to go for long walks any more, and you come to realise how easy it is to slip into a sedentary lifestyle. So I have set a goal to make no excuses, I will do my 30 seconds on the exercise bike four times a day.

One day a week I look after my baby grandson, so there is plenty of lifting, bending, and pram-pushing. Later in the day I walk to the school to meet his brother, who gets his exercise when he gets home by playing tennis or baseball on the Wii.

Everybody can do some exercise; if you are not physically disabled you have two choices - use it or lose it. Just do a little bit more each day than you did the day before, and you will sail into old age with your mind and body still in working order, and in perfect health. Exercise is the secret remedy for a fit and healthy old age.