A) the heel?
Recently, there is a movement that calls for "barefoot-style running" which promotes landing your feet on mid- to fore-foot. It is said this is the most natural way human runs before all those Nike, Adidas, Puma running shoes were invented.
When the running shoes were invented, we were told that landing on the heel was the correct way. Many "gimmick" running technologies were introduced to the market, such as air, shox, cell, etc to further lead us into using our heels as the first point of contact with the ground.
However, if you have ever run barefoot or on sandal, you would have realized that landing on your heel first hurts a lot! Unconsciously, you would change your way of running and land mid- to fore-foot. This further shows that evolution has made our feet to adapt to mid- to fore-foot stride running style.
From Popular Science: The Sole of a Winner
First of all, let's set the record straight. Man is a natural long distance runner. Despite impressions to the contrary foisted on us daily from our predominantly sedentary and "well-fed" modern lifestyle, it is interesting to note that for long enough distances a well-trained human can outrun just about any other creature on the planet.
Of course, recognizing the health benefits of exercise, not all of us live a sedentary life, and running has become a popular form of physical activity. In addition to the exercise aspects, however, those of us with a competitive or goal-oriented nature, from the elite athlete to the recreational runner, might be interested in running faster. Obviously accomplishing a 5K personal best or qualifying for the Boston Marathon requires a solid training program and a substantial amount of hard work. But what about those incidentals that might enhance our ability to train and thus augment our performance on race day? (We're not talking about performance-enhancing drugs here.)
That's where the video comes in. Running is a complex biomechanical phenomenon and this advertisement caught our attention because the design of these innovative shoes appears to seriously take some of the science into account. We are not endorsing a product here (especially since we haven't actually tested the shoes yet), however, let's analyze some of the issues presented in the video.
The major feature that separates these shoes from most other standard running footwear is that they force the runner into a mid-foot to fore-foot landing on each stride. Most running shoes have a large well-cushioned "heel counter" that makes it possible to strike the ground heel first without damaging the foot. While we do naturally walk heel first, it is true that heel striking is an inefficient way to run. Apropos of the video, let's apply Newton's third law. In order to land heel first, the foot must make impact in front of the center of gravity of the runner. This requires that the heel is going to push into the ground with a component of that force in the forward direction. The ground will then exert an equal and opposite reaction force, which means that there will be a braking effect on each stride. A mid- to fore-foot landing is going to take place more directly underneath the runners center of gravity alleviating this undesirable hindrance to forward motion.
In fact, consider the following: Man evolved to run barefoot, and shoes arrived on the scene only in the last few tens of thousands of years or so. Try running barefoot some time (preferably on a softer surface like grass) and pay attention to your foot strikes. You might find that it's almost impossible to land heel first. Your command central (your brain) just won't let you do it. Too much jarring. Your bare heel isn't designed to handle that pounding. The evidence supports that landing nearer the middle to front of the foot is the most efficient way to go. However, heel strikers should be advised that it might take some time to retrain your gait so that this feels at all natural. Trying to reform too quickly from a lifetime of heel striking could be a recipe for injury.
Finally what about those "actuator" thingies on the bottom of the shoe? The claim (put in more specific physics terms) is that they store elastic potential energy upon compression which is transformed back into kinetic energy upon push-off. While it is undoubtedly true that this must be happening to some extent, just like with a bouncy ball, the question remains as to what magnitude of an overall effect this could actually have. Let's do a rough estimate:
Exhibit A: The kinetic energy of a 75 kg runner moving at a speed of 4.0 m/s = ½ mv2 = 600 Joules.
Exhibit B: The amount of energy stored in a highly energy efficient spring (spring constant k = 1000 N/m) compressed a distance x = 1.0 cm (.01m) = ½ kx2 = 0.05 J.
Based on this calculation, it shouldn't surprise us that most of the elastic energy stored and released during the running motion takes place within the muscles of the body itself. The elastic properties of the shoes appear to be incidental and probably aren't going to make a lot of difference!
Nevertheless, one out of two ain't bad, and these shoes do represent one of the more interesting innovations in running shoe technology to come around in a long time.
A few weeks back we analyzed some of the features of the innovative Newton Running shoe in terms of the relevant physics principles. While at the time the point was to assess the theory behind the shoes, it was suggested that I put them to the test in my "lab." In other words, out on the roads and trails where, being of the distance-runner species, I generally spend at least an hour per day. While this is in no way any kind of systematic scientific experiment (which is beyond the scope of my resources), based on my personal experience with the shoes, I'll make an informal attempt to further address the claims made by the two Newtons (Running and Isaac!).
Let's address the two major issues from our previous article.
1) As we discussed last time, a mid- to fore-foot strike is a more efficient way of running than heel striking. Does running in the Newton shoes force you into a mid- to fore-foot strike?
That's easy. They sure do. It's those "actuator lugs" on the sole of the shoe, which make it very awkward to strike with the heel. You have to land mid-foot on the lugs or it feels like your foot is unnaturally tilting backwards. Running in the shoes does feel a bit odd at first, even for a mid-foot striker like myself, so if you try them, be aware they do take some getting used to. Because the lugs come down several millimeters below the rest of the sole, it feels like there's a small but perceptible mound under the ball of your foot, upon which you are balanced while running. As with barefoot running, you feel most comfortable in the Newtons when you run "light on your feet," landing mid- to fore-foot. However the feel is really rather different from barefoot running, due to that ridge of lugs underneath the ball of your foot.
2) As per the claim, do the actuator lugs really have superior elastic properties that conserve and return energy more effectively than "regular" running shoes?
This is a very interesting question, it turns out. According to the analysis from the previous article, physically it appears quite unlikely that the actuator lugs can store an amount of elastic energy significant enough to improve running economy. While the elasticity of the lugs may well be greater than in the sole of a traditional shoe, the amount of potential energy stored in the shoe itself will be negligibly small when compared to the total energy of the runner's stride. Does this mean that the claim of greater energy efficiency is bogus? Not necessarily! One thing that stands out for me while running in these shoes on a smooth hard surface (asphalt) is that during the time between foot strike and push-off -- that is, when my foot is in contact with the ground -- the lugs grip really well. There is no slipping.
If so, then it's possible that these shoes actually might improve running economy. My (highly subjective) experience during my test runs was one of less effort than usual at a given pace. This, of course, could be a purely psychological artifact -- maybe I was just excited to try out a new pair of fancy shoes. To really determine if this is true would require a controlled experiment with multiple runners over a long period of time. (Well worth the effort, I think, by the way!)
However, if there is an improvement in running economy compared to standard shoes, I hypothesize that it's not the elastic properties of the lugs that makes the difference. Rather, it's the friction between the lugs and the road that does the trick. Interestingly, while browsing the Newton website, I was interested to find that one of the features they advertise is low friction. I think that they're getting that one sort of backwards. A large amount of static friction between a running shoe and the running surface is a good thing. We're not talking about getting stuck to the pavement like a fly on some half-dried puddle of grape juice. We're talking about a no-slip foot strike.
With my current non-Newton shoes, I can often feel a small but perceptible slide during contact with the ground. The muscles have to work harder to make small adjustments every time this happens, which results in a decrease in stride efficiency. So with the Newtons, although the energy stored in the lugs themselves may not be a major factor in improving economy, the energy saved in the body due to less slipping -- the result of a large amount of static friction between the shoes and the road -- may well be.
Newton Running represents a relatively new innovation in the design of running shoes: an attempt to create shoes that facilitate a more natural and energy-efficient stride, an attempt to return us to our barefoot running roots without having to cut up our feet. Despite all of the cushioning and stability features of most "traditional" contemporary running shoes, the incidence of running injury is actually greater now than in the days of those primitive Pumas and Adidas. Is this because cushioned shoes with thick heel counters have taken us away from a more natural running stride? How well Newton Running shoes are able to resolve this and take us back to that ideal stride is not yet certain, but it's a worthwhile endeavor and a thought-provoking new option in the world of running shoes.
Finally, what of barefoot running itself, the true au-naturel version of the sport? Its devotees swear by it. Look for an investigation into this controversial topic a few weeks down the road!=================================================================
Terra Plana Vivo Barefoot
Vibram Five Fingers
Wetsuits Reef Walker
Popular Science: The Sole of a Winner
Popular Science: Tested - The Sole of a Winner
Society for Barefoot Living
Another interesting read about "The running shoe debate: how barefoot runners are shaping the shoe industry" from Popular Mechanics.