So here we are, in Bulgaria, just starting to rediscover the fitness we gained in Greece last winter - since lost in many long days of motorhoming, writing, talking. Fitness is a strange fellow traveller that can never be taken for granted. Sometimes it is with us; sometimes it slides away when we are not looking. Then, just riding the bicycles or walking the hills, we experience its slow return.

When we think that we still have it, setting off on some adventure, thinking that is coming along with us, we suddenly realise that it's not there, where we imagined it should be. Then, the next day, it appears again, or at least some of it, for a short time. This way, we learn how fickle it can be.

Sometimes, we don't even notice that we have it, until we walk or ride with someone who is without it. It seems that the fitter we are, the more we assume that it's a natural state. It's only with hindsight, when our fitness is at a lower ebb, that we can look back and say: 'goodness, we must have been fit to do that!'

Once we have had fitness, known its pleasures, felt its effect on the whole of our lives, enjoyed the speed and strength of our bodies, been aware of expanded and more efficient heart, lungs and muscle, we know it can never fully be lost.

What is for sure is that we can't buy it or borrow it and we can't pass it on to someone else. As the years roll by, we are happy just to have it hanging around, ready to be used!