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. Brefoot 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 generalizable 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 favored 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 there 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.
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.
Footstike 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. Fatigue: “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
-Ground contact time and footstrike related to running speed.
What it all means:
What does this all mean? It’s hard to make a lot of conclusions since the hard data on the british studies could not be evaluated yet. The preliminary observations are very interesting though.
In regards to foot strike, there is a relationship between running speed and footstrike. Do all fast runners forefoot strike? No, but there is a tendency for the faster runners to forefoot/midfoot strike more so than the slower runners.
Is this a function solely of the speed that they are running? Speed of running certainly plays a role in where you strike to an extent but it’s unlikely that it plays as much of a role as people make it out to. Meaning that someone is not going from a straight heel strike while running easy to a forefoot strike while running 800m pace. The Lieberman study provided the first evidence showing that forefoot strikers struck forefoot regardless of condition. Similarly, if we look at the data in the studies above, you can see that the percentage of footstrike types is remarkably similar despite the significant increase in average running speed (from 63-64sec per lap down to 57.5sec per lap). Even though these are different people running each event, if foot strike was solely a function of speed, like many have claimed, then you would expect to see a definite trend away from heel striking as the group got faster.
Perhaps most interesting is what seems to happen during fatigue. Ground contact times increase in both studies, regardless of footstrike. If we look back at what typically impacts ground contact time, it provides some interesting clues. Ground contact changed even when footstrike did not, so we can eliminate that possibility. The other two possibilities are that leg stiffness and use of elastic energy changed, which is entirely possible, but impossible to know. There is some research showing fatigue changes leg stiffness and stretch shortening cycle fatigue. Lastly, the most likely scenario is that fatigue is impacting the body’s ability to produce force in as short a time period.
Lastly, in the 1500m study it was interesting to see a change in footstrike pattern. During the last lap, you saw an increase in heel striking. This would seem surprising as generally one of the faster laps in the race as people try and kick it in. The question is why do runners switch to a heel strike under heavy fatigue? I’m not sure I have the answer. One possibility is that stride length tends to decrease with fatigue and runners are trying to compensate by lengthening their stride, but instead of doing it by pushing off and covering more distance, they simply let their lower leg reach out. Another possibility is that fatigue may impact fine control of the lower leg.
What do we learn from all of these studies?
It lends credence to the idea that footstrike is important when we are concerned with speed and speed only. There is a tendency for faster runners to adopt a non-heel strike in a variety of events. In addition, these foot strike types allow for shorter ground contact times, which also correlate well with speed. One other variable to consider is how that foot strike occured? It's impossible to know but where the heel strike took place is incredibly important. There is a big difference between striking close to under your hips to striking way out in front of you. Perhaps we should consider looking at foot strike in terms of where it occurs in relation to your center of mass, instead of where it occurs on the foot.
Using this data, I’d recommend a switch to a more midfoot or forefoot running style if speed is your main concern.
Secondly, these studies provide some interesting data on fatigue and foot strike. Seeing that ground contact times lengthen, some training should be done to avoid this decrease. I’ve written an entire article (and done a presentation, which I have not posted yet) on a related phenomenon, Strength endurance work, that explains some of the ways to combat this fatigue. We need to train the body to maintain force production (and muscle fiber recruitment) under heavy fatigue. This means start off with being able to increase force production, move to being able to produce force quickly, then move to being able to produce force in heavy fatigued conditions.
Basically, strength endurance work combined with plyometric and power training would seem the best way to train for this type of fatigue resistance. In practical terms:
-Strength Training -> Power training/ Sprint training -> Strength Endurance (Circuits/hills) -> Strength Endurance under fatigued conditions (hard circuits/ 200m reps at 800m pace w/ bounding in between)
Read more about Strength Endurance Here
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