I have been given a tool that could get me to that magic number. The Rola Backstretcher is designed to relieve back pain by stretching the spine. It also makes you taller - temporarily. It is a convex wooden frame with abacus-style rolling rungs. You lie on it. And if it doesn't work it makes a great magazine rack.
The inventor of this equipment is exercise physiologist Neil Summers who has Ankylosing spondilitis - a progressive and incurable fusing together of the spinal vertebrae that is supposed to turn you into an invalid. Sufferers are offered mirrors to hang around their neck so that when their chin hits their chest they can still see supermarket shelves. This was a grim prognosis for a 24-year-old Royal Marine.
Eleven years on, thanks to the Backstretcher, he can still enjoy visits to Tesco unaided. Recent trials at the University of Iowa Spine Centre confirmed its efficacy. Twenty minutes of bed rest lengthened the spine by 3mm. Twenty minutes of Backstretcher lengthened it by 13mm.
Of course, medieval torture equipment was more effective. But Summers assures me that moderate stretching relaxes muscle tension. With the Backstretcher, you can't overstretch. You shorten again, just as we shorten throughout the day as the vertebrae, which hydrate overnight, gradually compress.
In general, back problems shouldn't be ignored. Sixty per cent of us do or will suffer back pain, and 60 per cent us will have a diagnosable back problem. These two figures are not the same. Some people feel pain but shouldn't; some don't, but should. There is a big discrepancy. Some people feel better with strengthening exercises; some, like Summers, think stretching is the answer. Nobody really knows, and anyone who has had chronic or acute back pain will know how willing a sufferer is to try anything.
The NHS, by its own admission, knows next to nothing about what can be done for back pain, says Sarah Gordon, 32. Sarah has a misaligned pelvis, probably triggered by a childhood fall. Yet the pain only started last year. She regularly suffers complete seizure of the spine and sciatica that sends shooting spasms down the left leg.
"Apart from the pain, I hate the feeling of weakness, which has left me mentally very low. The NHS advice is complete rest, but I don't think lying down is best. You seize up, and that makes you weaker. You've got to keep going. That's why I believe in holistic therapies."
Sarah is now seeing a chiropractor. And if that doesn't work she will go to an osteopath.
"A diversity of ideas is best," says Dr Peter Skew, vice president of the British Institute of Musculoskeletal Medicine. "You need a combination of flexibility and strength to protect your back. If you hold the spine properly, the pressure on individual vertebrae is disseminated."
Of course, the real culprit of the back pain epidemic is our sedentary lifestyle: eight hours in front of a computer followed by four hours in front of the telly. Life was better for backs when the population of Britain was digging potatoes. But then, doubtless, I would have been writing a column on miracle cures for scurvy.
You can protect your back by keeping it flexible. "Think the shape of hot-cross buns," says Dr Skew. Stand up, from the hips lean forwards, backwards and then side to side. Repeat several times. Do this morning and evening and several times during the day.
The Rola Backstretcher costs pounds 82 from Enanef Ltd, Freepost SEA 4967, Dorking, Surrey RH5 6BR.Reuse content