Speed= Stride length X Stride frequency

This simple equation is a staple in sprinting and biomechanics material. It simply means that to see a change in speed you’ve either got to increase the ground you cover (stride length) or increase your turnover (stride frequency) or some combination of the two. The bottom line is that something has to change. But what is it that changes when we go faster?

If you are a Chi Running proponent, your answer will be stride length, as Danny Dreyer says to keep the frequency constant while only changing length. In the real world though, the answer is that it depends and that limiting yourself to only being able to change one or the other is a mistake. Let’s look at what the elites do.

One study looked at the stride length and frequency of the top 3 finishers in the 10k at the 2007 world championships. This included Bekele (1st) Sihine (2nd) and Mathathi (3rd). They calculated their individual speed, frequency, and length for every 400m lap of the 25 lap race. The graph below depicts their speed, stride length, and stride frequency:

The first thing you notice is that these three different athletes ran the same speed until the last 2 laps or so. That’s to be expected, but what is interesting is that they had different strategies to do it. Bekele had a low stride frequency with a long stride length for the first 9,000m. On the other hand, Mathathi had a small stride length and a very high frequency to run the same speed. Sihine was somewhere in between these two. What is also interesting is that Mathathi who is 1.67m tall and Sihine who is 1.71m tall both had considerably smaller stride lengths than Bekele who is only 1.60m tall. So, all you shorter runners complaining about how your height keeps you from having a long stride, just look towards Bekele. The point is though that we have three runners all employing different strategies to run the same speed.

It gets even more interesting when we look at the last 1km when the pace changed dramatically. For reference they went from hitting around 2:42-2:45 for each km to final km of 2:30, 2:33, and 2:36 respectively, and had last laps of 55.51, 58.66, and 62.16 so the pace picked up considerably. The question is how did these athletes do it?

Bekele did it by changing his stride frequency from roughly 190 strides per minute to an astonishing ~216 strides per minute, all while keeping his stride length about the same. So he went from having the lowest stride rate to the highest by far, thus using an increase in stride rate to increase his speed, while maintaining stride length. On the other hand, Sihine showed an interesting pattern. On the 3rd to last lap, he picked up his pace slightly with an increase in stride frequency. But then on the last lap, he increased his speed dramatically with an increase in stride length. The exact opposite approach of Bekele. Lastly, Mathathi, who had the shortest stride length, increased his stride length on the 3rd to last lap to increase his speed. What is really interesting is that on the last two laps, Mathathi’s stride frequency, which was the highest during the race, decreased slightly, while he increased his stride length significantly on the last lap. What this tells me is that he was suffering from the most fatigue and to compensate for the drop in stride rate, he tried to increase his stride length. The net result on the last lap was a maintenance of speed, not the giant increase like in the other two.

What does this all mean? Three different runners all had different ways of running at there race speed and then chose different methods of increasing speed when it was time to do. Interestingly, they seemed to increase the one factor that was lowest during most of the race. In Bekele’s case he had a low stride rate, so he increased that dramatically. Mathathi who had a small stride length tried to increase that during the final kilometer. And Sihine who was in between both during the race in terms of rate and length, did a little bit of an increase in both. It’s almost as if the runners subconsciously chose to rely more on rate or length for most of the race, to “rest” the other factor, and then went to the other factor when it was time to increase the speed.

This opens up a lot of questions, but before delving into those let’s look at one more study.

Sprinting- Stride length and Frequency

The above examples showed that there are several different ways to maintain a steady pace and different ways to increase the pace. But what about during maximum speed? Obviously when we sprint all out we are trying to maximally optimize the rate/length combination. Rate and length have an interesting relationship in that at max speed increasing one will lead to a decrease of the other, so it’s balance between the two that matter.

Which brings us to a study Salo et al. (2010) entitled: “Elite Sprinting: Are Athletes Individually Step Frequency or Step Length Reliant?”

In this study they looked at world class 100m dash competitions and calculated the individuals stride length and rate to see what the best athletes did. What they found was very interesting.

Individual athletes seemed to favor either longer strides or higher cadence. Just as we saw in the earlier study where Bekele versus Sihine and Mathathi adopted a different combination of length and frequency, it seems to occur in sprinters too. In the study, they found that individual athletes differed in their reliance on stride length. Some were very heavily reliant on having a large stride length, while others trended more towards relying on both, and even one athlete being reliant on stride frequency.

What’s interesting about this is that the author’s speculate that perhaps differences in the nervous system or power generation explains why some athletes rely on a longer stride or higher frequencies. For sprinters who are powerful athletes and can generate a large amount of force through their stride, they are more likely to cover more ground with each stride, thus being stride length dependent. On the other hand, some sprinters seem to rely on the nervous system’s ability to rapidly turn the legs over and contract and relax the muscles extremely quickly, thus making them more reliant on stride frequency. Driving this point home, the author’s stated that “Thus, it is possible to reach the absolute top level of sprinting in the world (run under 10.00 s) with widely varying pattern of SF and SL reliance.”

In recent years there has been a trend towards focusing solely on maximum force production as a way to train sprinters. It was fostered by Weyend et al.’s early 2000’s study that showed sprint speed was partially determined by vertical Ground reaction forces. Some coaches took this to mean that the only way to increase speed was to increase force production. In the Salo et al. (2010) study they mention that increased ability to produce force has been shown to be a determinant of stride length in animal models. What the current study shows us though is that for some athletes the limiter is not force production, but how quickly an athlete can contract and relax the muscles and ultimately turn the legs over faster. The author’s conclude by saying:

“Overall it is reasonable to conclude that SL is related more to increased force production, and SF is associated with faster force production during the contact and quick leg turnover requiring neural adaptations. Higher SF requires cross-bridges within the muscles to be built at high rates, and thus these need a high rate of neural activation.

Consequently, it is proposed that the SF reliant athletes are required to concentrate on neural activation in their final preparations for the major races and have a nervous system ready such that they can produce the quick turnover of the legs. On the other hand, the SL reliant athletes need to keep their strength levels up throughout the season and have the required flexibility in the hip area to produce long steps. Naturally, athletes cannot totally forget the non-reliant variable, as any disproportionate reductions in one variable cannot be generally compensated for by the other variable.”

Another interesting fact, which we saw in the 10k study too, is that the height of the athlete did not impact whether or not they would take longer strides or have a higher cadence.

Putting it all together

The point of this is to show you that there are many roads to running the same speed, whether it is sprinting or running a 10k. What the above studies show is that perhaps it is highly individual. Runner’s like Bekele may have adaptations that lead to him being able to hold a massive stride length for a long time, and then switch and be able to hold a large stride rate during the latter stages of the race.

The question is should we individualize based on our preferred method of running? Stride length dependent athletes might need to do more strength/power work, while stride frequency athletes might need to do more turnover work/neuromuscular work. Or should we work on our weaker side of the equation? The ultimate answer for us distance runners may be that we should be like Bekele and be able to run submaximally with one strategy and then be able to switch strategies when fatigued. Maybe this is why he can kick so well? He’s able to run both ways.

The great Hungarian coach Mihali Igloi was a big fan of what Bekele seems to have done in the 10k. Igloi believed that runners had a natural stride they preferred, but then should use their “unnatural” stride during heavy fatigue. He called them short swing and long swing strides. Short Swing would be equivalent to a shorter stride length with a high frequency, while long swing would be a long stride with a reduced frequency. His contention was that you needed to work on going back and forth between these two stride types during practice. If you could become adept at using both strides, then you could run the majority of your race in your preferred stride style, but when fatigue started to happen, you’d switch to the other stride style. His contention was that by switching, you are changing the muscle fibers that are recruited slightly, and you are also changing how they work (powerful as in a long swing stride, or rapidly as in a short swing stride). In essence, this is what Bekele did. He went from a long swing to a short swing style in the final kilometer.

Hopefully this mini stride frequency versus length topic makes you think a little bit. In particular it should be obvious that there is no magic stride frequency that everyone should run. It depends on the athlete and their speed. Some rely more on stride length, while others will rely more on frequency like Mathathi. But you have to be able to change but frequency and length throughout the spectrum of running speeds. If you, like Chi running advocates, try to hold one constant, you’ll reach your limit in increasing the opposite one before you should, and thus will be slower. In an ideal world, you should train to be able to do both when needed. Perhaps that’s what makes Bekele the man to beat on the kick?

References:

Salo et al. (2010) Elite Sprinting: Are Athletes Individually Step Frequency or Step Length Reliant? Medicine and Science in Sport and Exercise

Enomoto et al. (2008). Biomechanical analysis of the medalists in the 10,000 metres at the 2007 World

Championships in Athletics, New Studies in Athletics

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