Ever since I started running in 1986, many common injuries have come and gone without seriously threatening my existence as a runner. I suspect this is something a lot of long-term runners will recognize. From about 2006 on though, I began to get occasional problems with a knee that were more scary, and around 2009 this got so bad that for more than a year I was convinced I would never run again.
Still, after some physiotherapy and a forced interruption by a herniated disk and operation I managed to get going again late 2011; a sinister pain inside the knee kept coming back, however, and I feared this was the beginning of arthrosis (which occurs more in our family, in the same knee and side of the knee) and would eventually end my running career for good.
Then, in 2014 I came across a number of sources that inspired me to reform my training method and running technique such that running would put less strain on the knees, and gave hope that my running existence could not only be extended by many more years, but that I could also become better and faster than before. Hereafter I will briefly explain the adaptations I have made that seem to work; that is, that enable me to keep running without causing knee problems, and/or even make me faster.
As my new training approach, I (largely) adopted the Souplessemethode, which is explained in a book by the Netherlandic former runner Klaas Lok, who in turn based it on the method of his former coach Herman Verheul. Lok is working on an English translation of the book. My experience so far is that I become faster, be it that this way of training is more strenuous for the muscles and tendons in the lower legs. I managed to adapt to that by carefully controlling the contents and frequency of the sessions.
The method is based on interval training of moderate intensity (just under the anaerobic threshold) with fairly long recovery breaks and not too many repeats. Traditional endurance runs are avoided, occasional endurance runs with tempo variations are included but do not form the core of the method. This way of training is, in the neuromuscular respect, similar or identical to the way one runs in races. The method agrees well with me, and in fact I tend to stick to the interval sessions and avoid endurance runs almost entirely. For a detailed description of the method, see Klaas Lok's book and web site.
The Souplessemethode prescribes no particular technique of running, but does advise shoes with "zero drop" (that is, heel and forefoot/toe on the same height) and less or no shock absorption, and naturally leads to a light-footed style with forefoot or mid-foot landing. This led me to study two published running technique methods, the Pose method of running and ChiRunning. Both are instructive. There is an overlap between them, but there are also differences. I lean more toward the Pose method, but have used elements from both to improve my own style. I have not adopted either method entirely. For details of the methods, see the relevant books and web sites, which are easily available. My current running technique is as follows:
Both the Souplessemethode and the Pose method recommend footwear with less or no shock absorption and "zero drop". Such shoes facilitate forefoot landing, while regular running shoes with thick soles and raised heels invite or even force one to let the impact be absorbed by the heel. These "minimalist" or "barefoot" shoes are associated with what one nowadays calls "natural running".
I have switched to more or less minimalist shoes, and run mostly on half-minimalist ones that have some shock absorption, but less than normal running shoes. Now and then I run on full-minimalist shoes with as good as no shock absorption. These latter shoes, and the corresponding running style, take quite long to get used to, like months to a year. I find it is well possible to run without discomfort on shoes with no shock absorption, as long as I go rather slowly. But at a higher pace, like in interval training, I still prefer semi-minimalist shoes because of the higher impact at those speeds. I do not run on normal running shoes any more; neither do I ever run literally barefoot, as some do.
Perhaps surprisingly, full-minimalist, "barefoot" shoes are highly suitable for running (not too fast) on hard flat surfaces like asphalt; the forefoot landing style cushions the impact well enough to make shock-absorbing soles superfluous, and the hard surface gives immediate feedback when one hits the ground too hard with the heels. Paradoxically, on natural, unpaved terrain, these shoes give occasional problems because small, hard, sharp objects like pieces of rock or gravel penetrate the thin soles and hurt the feet. On such surface, the somewhat thicker semi-minimalist soles give better protection. For faster running as in interval training, I always avoid hard surface and prefer gravel, grass, and sand.
An effective measure that has helped to adapt to the higher strain on muscles and tendons in the lower legs is reducing training frequency. The greater recovery time thus obtained prevents injuries, for instance of the achilles tendon. Meanwhile, the new running style and training method make the involved tendons and muscles stronger, so that I may be able to raise the frequency later on again. I have gone down to one running session a week. The time thus freed I partly fill with walking, so that I have to some extent replaced the former long slow distance runs by walking. I walk fairly fast, with a technique compatible with the Pose and Chi methods (which have walking variants too).
In addition to running, I do exercises as described in Exercises for knees, back, and neck. Also, I am taking a qigong course; this concerns a Chinese system of physical exercises related to and including tai chi. In these exercises, one has to keep the abdominal muscles tightened and pelvis aligned correctly, like in running, and since that is particularly hard for me, the extra attention thus given to it helps to learn to maintain the correct position.