It is the Holy Grail of running: how to run - and run - for months and years on end without getting injured.
Most runners wear the right shoes and most runners stretch, but despite all these precautions, they still get hurt. Calves and ham-strings get tighter and tighter, curdling into little knots until eventually they snap altogether PPP-CHOINGGG, and then... then you'll know all about it.
Knees can also give out, as can ankles and hips - particularly if you do a lot of road-running. I have one friend who was once a superb marathon-runner, but who can now only walk with sticks. "Run on the grass!" he counsels as I scamper past his garden in Inverleith in Edinburgh. "Don't run on the pavements!"
There are a few other things that can help you stay injury-free. I'll come to them shortly.
But there is also one golden secret to not being injured. I call it a secret because even a lot of seasoned runners have never come across it before. They have no idea what a powerful running tool it can be.
For myself, I'd been running for well over a decade before I first came across the golden secret five years ago. I was training for the Marathon des Sables, in the Sahara, and one of the absolute keys to finishing this extraordinary race is to stay injury-free.
I stretched, I had sports massages, but as I started to put in the serious miles, sometimes over 100 miles in a weekend, my legs just got tighter and tighter.
And then Dean, my physio and my sports guru, gave me one beautiful tip. It is cheap and it is brilliant, and - touch wood - it's kept me injury free for five years of marathons and ultra-marathons and even the Marathon des Sables. (Blisters excepted - but there's no avoiding blisters in the desert.)
First though: some of the basics to staying injury free.
1. Get the right shoes. This is easy! Just go to a specialist running shop where for a bargain £20 they will analyse your running gait and tell you the shoes that are right for you! They'll tell you whether you're an over-pronator or an under-pronator of whether your feet are just perfect. Buy the recommended shoes - and next time you need a pair, just go onto the internet and get them at half the price. Easy!
2. Keep off the tarmac. If at all possible, run on grass rather than roads and pavements. This won't make much of a difference initially. But after a few years, road-running can have a huge impact on the general wear and tear of your legs.
3. Stretching. We love stretching! Stretching after you've warmed up! Stretching after you're done! Don't bounce those stretches! The longer you hold that stretch, the better! If you're pressed for time, then cut a mile off your run rather than miss out on your stretching!
4. Yoga. I started going to yoga classes three years ago and once you've got over your initial squeamishness (if you're a bloke) they are brilliant for staying supple. Rather than just a ten-minute stretch at the end of your run, you're stretching for over an hour - and are sometimes holding the most agonizing poses for a couple of minutes. At times excruciating. But brilliant for your physical and mental well-being.
5. The Golden Hour. This is crucial if you are putting in a lot of miles, as it greatly aids your recovery. All the seasoned runners on the Marathon des Sables were doing it. (The Marathon des Sables is happening just this week, by the way. Think of all the tears and the blisters, and the intoxicating euphoria!)
Two things you've got to do in The Golden Hour - and they both have to be done within an hour of the end of your run.
First: get some food inside you. Food is much, much more effective if it's eaten soon after you've stopped running.
Second: put your feet up. Lie down on your back and put your feet on a chair or a sofa so that they are about a foot off the ground. Leave them like that for 15 or 20 minutes, dream dreams of running the Sahara, and let the lactic acid and other such junk drain out of your legs.
That's it! The Golden Hour. Simple yet effective.
6. Sports Massages. If you're running over 30 miles a week, then try a sports massage. They are probably the most pain you can get for £50 an hour.
Sports massages help iron out the knots that, despite all your best stretching intentions, start to accumulate in your legs.
Me? They hurt - and I can take quite a beating.
The great Dean, who is a well-muscled man, would begin with the heels of his hands before eventually gouging into my legs with his elbows. Yowweeee!
And finally... after a modest build-up, we come to The Golden Secret of Injury-Free Running. This is what I know to be true.
If you want to be an injury-free runner, then get yourself a sports roller - available on Amazon for under 15 quid.
You might have seem them being used down at the gym, people grunting away as they lie on these strange foam rolling-pins. They may look perfectly innocuous - but they are the absolute key to keeping your body in good nick. Much, much more effective than mere stretching.
Rollers are about eight inches in diameter, and between 18 inches and three feet long. (There are hand-rollers, like little rolling-pins which you work up and down your legs with your hands, but they are not nearly as effective as a full-size roller. )
There is some technique to using a massage roller, so get a pro to show you the way.
But all you're basically doing is lying on the roller and letting your full bodyweight squeeze down onto your leg or back or whatever other body-part is being rolled out. You move backwards and forwards, letting the roller work at your leg muscles; if you've been for a long run, it is really painful. It's squeezing out the knots, squeezing out the lactic acid and stretching you like nothing else.
There are a number of different types of roller - simple foam ones which aren't quite so painful and then all the way up to rollers with serious, hard knobbles. As a rule of thumb, the more painful it is, the better it is for you.
Now: here's the clever bit. This is what I know.
To get the full benefits of a sports roller, you want to be using it every day. You want to be on the roller even when you haven't been out running.
And that means... making it part of your daily routine.
It's a really easy routine too. Instead of just sitting on the sofa when you watch TV, you put in 10 minutes on the sports roller.
And that's all there is to this wonderful golden secret: Ten minutes on a sports roller. Every day.
And though we make no promises, and though accidents can always happen, this is going to give you your very best shot at being an injury-free runner.