My Auntie Viv, who is an extraordinary person and just finished an M.A in Fine Arts, had a problem with her knee. So went to her doctor and he said that it was wear and tear. She told him that this was ridiculous because she'd had two knees for the same amount of time so there was no reason for one to wear out but not the other.

So I thought about this and started to observe my knee use. Did I use them equally? Did I heck as like. No, I have a leading leg, and it's my left. When I walk up stairs I go left first, so when I walk up kerbs, my left leg does the work. If all staircases had equal numbers of steps we'd use both knees equally, but I think it's kerbs that do it, kerbs and steps up to people's houses, which often have one or three steps. Don't know why, but check for yourself. So if we continue to step up with our leading legs without thinking about it, it stands to reason that one will wear out first.

Today, for Tuesday. I'm aiming to do things with the other side from usual. For example, pressing the space bar on my computer keyboard with my left thumb instead of my right. Try it; it's hellishly difficult. But I've had right thumb injuries - ldeading all the way to my shoulder - and I think this is what's caused it. I've aldready had to switch mouse sides. As I played the piano for years I'm closer to ambidextrous than most, but this is tricky. Even putting my socks on the other side first took some serious concentration.

Tonight I shall be teaching yoga at the hall down the road. We spend a lot of time in yoga balancing both sides of our bodies because it helps to balance our minds. If you do a yoga posture on one side then come back to the centre it feels seriously odd, as if one side of the body is awake and the other is still snoozing. After all that we do tend to come out feeling mentally balanced at the end of a class.

So for reasons of practical joint wear and tear, and to aim for a calm, balanced approach to life, have a crack at left-right equality. Carry your bag with the other hand. Some things we can't change, like where the brakes are on a car or the Oyster pads in a tube station, but otherwise, put the balance back and see how you feel at the end of this Tuesday.