Thursday, 10 June 2010

Touch and Go #10

Posted by speedygeoff on Thursday, June 10, 2010 with No comments
New studies on footstrike. Do faster runners heel strike?
Perhaps the most interesting finding in Lieberman’s work is that it may not be so much the barefoot vs. shod but the footstrike that is the important part. Barefoot running allows for the footstrike to happen properly, so they are interconnected.

Let’s leave behind injury prevention for a bit here and focus on speed. Is one footstrike better for speed in distance events? There are several theoretical arguments that point towards yes.

The role of elastic energy storage and return is one such factor. I’ve already mentioned this quiet a bit, but the Achilles tendon and the arch of the foot store a large amount of energy upon footstrike and then that energy is subsequently used upon take off. A forefoot strike has shown that it potentially uses this mechanism much better. One reason is that upon initial contact the foot is in better position to store the energy from the ground strike. In heel running, a great deal of the initial strike energy is lost. On a similar note, it is possible that a forefoot strike utilizes the stretch reflex mechanism better due to the position of the foot upon contact. With a forefoot strike the whole calf complex is in better position to be stretched and subsequently respond than in a heel strike.

Another potential performance enhancement is that it allows for shorter ground contact time while applying the same amount of force. Several different studies have shown the importance of ground contact time in running. In two separate studies, shorter ground contact time was correlated with top running speed and better economy. This shouldn’t be a surprise when you think about it. Ground contact time is going to be a result of mainly the person’s ability to produce force quickly, footstrike, and the ability to use the elastic energy mentioned above. Obviously footstrike plays a role in the latter two.

Let’s look at a couple of studies on footstrike. Several of which have yet to be published.

In the one study that everyone quotes, Hasewage 2007, they looked at footstrike at the 15km mark in a half marathon. The anti-forefoot strike people use this as justification in their decry of changing running mechanics. However, there are several problems with this view. First, let’s look at what the study said. In the study, out of the 283 runners, 74,9% were rearfoot strikers. The rest were midfoot and forefoot strikers. That leads many to conclude that rearfoot strike may be the way to go. However, if we look at a couple of other factors the picture gets a little more cloudy. When you separate out the top 50 instead of using the entire group, those who midfoot or forefoot strike jumps from ~25% to 38%. That significant difference showed that there was a tendency for more mid/forefoot strikers to be faster.

Secondly, if we look at ground contact time, there was a linear relationship with the faster runners having less ground contact time and GC increasing as you got slower and slower. Basically, the faster the runner, the lower the GC, this isn’t unexpected. In addition, forefoot/midfoot strikers spent significantly less time on the ground than their heel strike counterparts (183ms vs 199ms). These findings led the researchers to conclude:

“The percentage of RFS increases with the decreasing of the running speed; conversely, the percentage of MFS increases as the running speed increases. A shorter contact time and a higher frequency of inversion at the foot contact might contribute to higher running economy.”

There are still two other factors that no one takes into account. First off, the video was taken at ~9.3mi into a 13.1mi race. In other words it takes place pretty late in the race when fatigue has already set in. Studies have shown that footstrike changes with fatigue. What happens is that more midfoot and forefoot strikers become heelstrikers. Thus, when you look this deep into a race, that potentially skews the percentages.

Secondly, the study was done in a large Japanese road race. While there were several elite Kenyans and other nationalities, of the top 283, the vast majority were Japanese. This is very significant. This means that technically, the results are only generalisable mostly to Japanese runners. Why is this significant? Because of how the Japanese historically train and how they historically run. Due to the heavy emphasis on very high mileage and moving everyone to the longer distances (half marathon and marathon) with neglect to the shorter distance races (1500,5k), the running style of Japanese runners is much different than Americans, Europeans, and even Africans. Similarly, the traditional ideas taught by Japanese coaches at the time favoured a running style that was more flat/scoot around type running. Researchers and scientists will probably scoff at this idea, but go watch any video of top Japanese running and you will notice a visual difference. In addition, one of my coaching mentors started spending time going to Japan educating Japanese coaches on running mechanics at around the time of this study. We’ve spent many hours discussing what their views were, what the runners were being taught, and how their athletes were running.

Due to these factors, it’s impossible to take this study and generalize it to anyone except Japanese runners. In addition, the study shows that speed is correlated with both footstrike and ground contact time.

British studies:
In all of the British studies they looked at semi-elite/competitive runners during 800 and 1500m competitions. They looked at foot strike and ground contact time on each lap. This will not only give us an idea on foot strike implications but also on fatigue. The conclusions that can be drawn based on the research about fatigue and training are very interesting!

In the 1500m, the range of times went from 3:45 to 4:22 with the average being 3:56.
Once again, ground contact time-ground contact time was related to foot strike. Forefoot strikers spent 161ms on the ground compared to 169ms for midfoot and 192ms for heel strike. The difference between heel strike and the other two are pretty remarkable. What is interesting is that ground contact increase basically on every lap.

Footstrike also changed based on lap. Initially on lap 1, 34.6% were forefoot striking, 46.2% midfoot, and 19.2% heel striking. On lap 4 the picture changed slightly. More of the midfoot strikers in particular had switched to heel striking (heel striking increase to 27%.)

What this means.
: “over the course of a 1500m race, ground contact time increased irrespective of footstrike position. This implies an element of fatigue, with runners presumably requiring longer to generate the same impulse.”

Before delving into the meaning of this, let’s look at the results of the other study on 800m runners quickly:

800m male runners
- 1:47 to 2:01 (avg: 1:55):
- forefoot-35% Ground contact (156ms)
- midfoot-48% Ground contact (161ms)
- Heel-17% Ground Contact (177ms)
- Ground contact lap 1- 156ms lap 2-168ms

from Science of Running by Steve Magness. To be continued...



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