Running shoes Part III

Running shoes, barefoot running and muscle tuning: The intelligent biomachine and implications for running

Well, it's been a week and a half, and an interruption of our series on Running Shoes thanks to Gebrselassie's announcements, but I have finally managed to get back to the topic that had caused so much debate and discussion: What is the value of running shoes? Do they cause more problems than they fix, and what is the future of the running shoe industry?

One argument that has been put forward a great deal is that barefoot running is the way to go. Apart from the obvious practical concerns - glass, stones and other objects not meant to be run on by 'soft' feet - I'm not 100% convinced that the knee-jerk reaction in the opposite direction is the way to go either. I know podiatrists who are of the opinion that the sole function of the shoe should be to protect the sole of the foot, which is in line with what we've been discussing, but a more extreme argument.

I'm sure there's merit in that argument, but I wouldn't dare suggest that any reader of this post suddenly switch to barefoot running, or even to lightweight trainers if they've always worn more supportive motion-control shoes - remember, the key to successful training is managing change, and physiologically, you'll pay a hefty price if you make a drastic change like this. Instead, the objective should be to manage the change, aiming to gradually move away from the bulky shoes and into the well-cushioned one. This requires changes in training, possibly strengthening exercises to correct weaknesses and imbalances that predispose to injury, and then the new shoe should work.

However, the debate between barefoot and shoes is nevertheless interesting, so a few interesting discussion points that arise are considered below.

Biomechanics of shoes vs. barefoot

You have no doubt heard, read or experienced that one of the main differences between running in shoes and running barefoot is that when you run barefoot, you tend to land more on the front part of the foot. In contrast, pull on a pair of shoes and you'll land more on the heel. There are of course other differences - barefoot running tends to have a shorter contact time, a shorter flight time, lower impact forces and higher muscle activation in the calf muscles just before landing. You also land with your ankle more "pointed" (called plantar flexion) as opposed to dorsiflexed, or pulled back towards you. But the argument around landing on the heel vs. ball for shoes and barefoot running is one of the more common ones, and certainly less technical!

The "heel-strike" observation forms the basis of many people's arguments for why a forefoot landing is better than a heel-strike. The problem is, people often get trapped by their own logic when discussing this concept. The thought process when it comes to barefoot vs. shoes is often the following:

1. Barefoot running is natural
2. When you run barefoot, you tend to land on the ball of the foot, whereas in shoes, you land on the heel
3. Therefore, landing on the forefoot is "natural" and good, but landing on the heel is unnatural and thus bad.

Apart from the assumptions of what is "good" and "bad" in all this, there is a hidden question that must be answered first:

Why does the body allow the landing to change simply by pulling on a pair of shoes? Or, looked at differently, if you take off your shoes, why do you suddenly land on the ball of the foot?

An intelligent system - changes in mechanics serve a purpose

The answer to this question must be that when you take your shoes off, your body is "intelligent" enough to adjust your landing in order to reduce the loading force and rate. The change in biomechanics thus serves a useful purpose! This is a conclusion made in many studies. For example: "...barefoot running leads to a reduction of impact peak in order to reduce the high mechanical stress occurring during repetitive steps" (Divert et al. Int J Sports Med 2005). This reduction is achieved in part by changing muscle activation (which we'll come back to), as well as altering the biomechanics slightly as described above - lower flight, different ankle position on landing and so forth. The end result is that you land more on the ball of the foot.

Of course, what people often forget is that if it works this way - taking shoes off - then surely it must work the other way, when you put the shoes on? In other words, when you run in shoes, your body is "intelligent" enough to recognize the added cushioning, and so it allows you to land on the heel. There's no reason to suggest this is bad, but applying the same logic used above, it might actually be a beneficial, positive response to wearing shoes - perhaps landing on the heel is the protective, optimized adjustment to running in shoes?

It's never made a great deal of sense to me, but the key is, the body seems quite capable of changing mechanics and even muscle activation in order to reduce impact forces - and this introduces the concept of "muscle tuning".

Muscle tuning - adjusting for impact

The concept of muscle tuning, proposed by Benno Nigg in Calgary, is both new and quite complex. And I'm certainly not a biomechanist, and so the detail and technical explanations are best left out of this discussion! But the concept has some quite important implications, which we'll get to.

First of all though, muscle tuning is the adjustment of muscle activity in response to impact forces, and it ends up minimizing soft-tissue vibrations and joint-loading. Let's step back a little - when you are running, the muscle is activated BEFORE you land in order to prepare the joints and supporting structures for the impact. This muscle activity is called pre-activation and there's actually a good deal of evidence that suggests that performance is influenced by this pre-activation, since it helps to store up elastic energy and make running more efficient. The muscle is then active during the entire stride, after ground contact, to continue to support and control movement of joints.

What Nigg found is that when you run in shoes with a softer or harder midsole, or run at different speeds, you change the impact forces, but the muscle activation simply compensates and you end up experiencing similar soft-tissue vibration. In other words, your body is "intelligent" enough to adjust muscle at different levels to ensure that you don't have excessive joint loading and tissue vibration.

Where this becomes especially relevant is in the application of the theory to orthotics, running shoes, and other shoe inserts. Because this theory is saying that the muscle activity during running will increase as soon as the "preferred" movement is affected. The use of running shoes, for example, which may well alter the movement of joints during running (think anti-pronation shoes here), will then simply produce an increase in muscle activation which now stands to affect the body's "natural" mechanism to regulate joint-loading.

So in effect, the problem with shoes, orthotics and inserts might actually be that they promote an increase in muscle activation, which prevents this "intelligence" from regulating the normal soft-tissue vibration. Nigg suggests that things like orthotics and shoes should reduce the muscle activation in order to be optimal, rather than increasing it by preventing normal movement. Quite how one establishes this outside of a specialized biomechanics lab is a tricky problem, but that's another matter.

How much do all our interventions (and inventions) actually achieve?

The point for the running shoe industry is to recognize that the best efforts of researchers, product developers and (we have to point out) marketing experts, may in fact be trivial by comparison with the remarkable ability of the human body to adapt and respond to "stress", whether that stress is changing running shoes or long term training.

Of course, problems do develop and injuries do happen, and when they do, it's fascinating to wonder whether in fact the cause might be the change that we try to introduce to fix the problem! Is it possible that clever product development, based on theories and concepts, have actually forced the body into a "wrong" response that has increased injury risk in the long term? And is there a chance that if we just left physiology to its own devices, and managed every case individually, we'd be better off?

So to continue the theme of the running shoe, the shift in the industry has without doubt been towards a more "natural" shoe. Of course, they can't sell "barefoot" (that's free!), so the next best thing is to be barefoot in shoes, which is where it's going. Practically, however, the challenge for everyone is to manage that, and not simply leap from one extreme to the next, as mentioned above.

That's it for shoes for a while, we'll no doubt come back to the topic in the future. But next on the agenda is a series on performance, the brain and pacing, which throws up some fascinating questions and hopefully discussion. So join us then!

Ross