Despite lingering constriction of the throat and sore ears, I decided it was time to recommence moderate intensity running today with three 1Km repeats at 5K pace (around 4:20 min/Km ). I did the first two repetitions in 4:20 and 4:21 at mean heart rate 142 and 143. Then during the third, the cold air upset my airways and I started to develop an asthma attack. I completed that repetition in 4:32 at HR 144, and jogged home. I had taken one puff of my long-acting inhaler early in the morning, but it appears that in this weather I should increase the dose. Nonetheless I was quite pleased that despite my recent bout of flu, my pace and heart rate in the first two repetitions were similar to the recordings in a 6x1Km session on 6th December.
This a picture of the Trent beside the path where I do 1Km repeats, taken in May of this year. Ignore the incorrect date setting on my camera.
I had started this year with the intention of developing a running style that minimised risk of injury, especially the risk of further damage to my right knee which has been ravaged by intermittent attacks of inflammatory arthritis since childhood. I have read fairly widely and been influenced by an number of authors, especially Gordon Pirie, and to a lesser extent by Nicholas Romanov, the inventor of the Pose technique. Some of the principles of Pose appear to violate the laws of physics, especially the laws of conservation of energy and momentum, but despite its shaky theoretical foundation, the experimental evidence confirms that Pose places less stress on the knee. The study by Arendse and colleagues from Tim Noakes laboratory in Cape Town demonstrated a 50% reduction in work done at the knee joint when running Pose style compared with heel striking. So I attempted to work out a rational basis for a running style including what I regarded as the good features advocated by Pirie and by Romanov, but with a rational foundation based on the laws of physics. The details are described in the articles in the side bar entitled ‘A dance with the devil’
Unfortunately I have had a somewhat disappointing year, mainly due to respiratory problems, and it is difficult to judge whether my running style has been a success. The good news is that my knee is coping fine. It has caused far less trouble this year than it did in my mid-fifties before I recommenced running; and also, less trouble than last year, when I had remained injury free for most of the year, but suffered a flare up of arthritis in late summer that caused me to descend stairs on all fours for a week or so. That was the final impetus to develop a safer running style.
While my knee has been virtually trouble free this year, I have suffered two minor injuries. In neither case was running style the main cause, though in each case, I think that my new style did exacerbate the problem.
One of the crucial features that I learned from Pirie and Romanov is the principle of lifting the foot from stance as quickly as possible. This ensures that much of the energy stored in the muscles, tendons and ligaments at footfall is recovered via elastic recoil. Because muscle and tendon is viscoelastic, recovery of energy is greatest when recoil is rapid. The time on stance should be around 100 milliseconds or less. If cadence is around 180 steps per minute, which experience indicates provides optimum efficiency, the duration of each stride is 333 milliseconds. Therefore, when time on stance is less than 100 milliseconds, the major part of the stride is spent airborne. The vertical ground reaction force that must balance the downwards impulse of gravity acts only for a minor fraction of the gait cycle, and hence this ground reaction force will be several times body weight. For cadence180 steps per minute and time on stance of 100 milliseconds, the average vertical ground reaction force will be three times body weight, and for shorter times on stance, it will be even greater.
Another, more controversial feature borrowed from Pirie and Romanov is that it is most efficient to land on the forefoot. If vertical reaction force is over three times body weight, this places a substantial load on the ball of the foot. In addition, a substantial tension develops in the Achilles tendon. If the knee is slightly flexed at the time, a large portion of this strain is taken by soleus, the deeper of the two calf muscles. Unlike the larger gastrocnemius muscle, soleus does not cross the knee. Hence when the knee is flexed, tension in gastrocnemius is low and soleus bears the main burden.
So how did the principles I borrowed from Pirie and Romanov contribute to my injuries? The main culprit for the first injury was a stone on the path. I landed with the stone beneath the head of my second metatarsal, and a force greater than three times my body weight was transmitted directly onto the metatararsal head and adjacent metatarso-phalangeal joint. Ouch! This part of my foot has always been vulnerable and I was hobbling for several weeks afterwards.
The other injury occurred when I made a fairly rapid increase in the intensity of my training. After several months of low intensity training, I did two speed sessions within a week. In the second session, while running fairly fast uphill over irregular ground, I suffered a minor tear of soleus. Undoubtedly the main culprit was increasing intensity too quickly. I had not conditioned soleus adequately for the task, so I do not think that I should lay too much blame on my change of running style. However, this injury emphasises the importance of conditioning soleus well before increasing training intensity. It also suggests that when running longer distances, it is best to allow the heel to touch the ground in mid stance to avoid the risk that repeated micro-tears will combine to produce a full-blown tear of the muscle.
Despite the occasional tribulations, I am still greatly enjoying running and looking forward to an even better year, next year.
Happy New Year and good running in 2009.