Other than recommending this book as a great vacation read or a way to rekindle your passion for running, I’d like to concentrate here on one of its central claims about the biomechanics of barefoot running, because it resonates so strongly with the thesis of Hormetism and Edward Tenner’s theories about the “revenge effects” of technology — and because it has implications that extend well beyond the sport of running. McDougall’s seemingly paradoxical assertion is that running without shoes makes one less susceptible to injury than using modern engineered running shoes, with their high-tech cushioning. Says McDougall: “Running shoes may be the most destructive force ever to hit the human foot.” (BTR, p. 168)   …How can this possibly be true?

Perhaps the most controversial thesis of McDougall’s book is that humans evolved to be long distance runners, and that at some point in our evolution as hunters we exploited this ability to actually run down large game such as antelope–animals that could outsprint us for short spurts, but would eventually tire and give up.  McDougall cites some archeological and biometric evidence, but I’m not so sure I buy this, and I’m somewhat skeptical and weary of the constant invocation of evolutionary arguments to explain just about everything related to diet, health and fitness. It’s just that it is so difficult to verify these speculations, so  I happen to prefer more testable explanations based upon physiology. And in the area of physiology, I believe that McDougall is onto something. The idea that adding padding or protection can hurt or injure us seems to be a paradox–at first glance.  But if we can understand why protective armor has this effect, perhaps it can teach us something about human adaptation that extends beyond the domain of running.

Shoes and foot injuries. Among the many experts McDougall cites, Stanford track coach Vin Lananna has a certain credibility when he states: “I can’t prove this, but I believe when my runners train barefoot, they run faster and suffer fewer injuries…We’ve shielded our feet from their natural position by providing more and more support…If you strengthen the foot by going barefoot, I think you reduce the risk of Achilles and knee plantar fascia problems.” (BTW, p. 169-170).  Dr. Barry Bates, who directs the University of Oregon’s Biomechanical/Sports Medicine lab, gathered data showing that the cushioning on shoes does not reduce impact on the legs, but may actually promote injuries. To gain insight into why this should be so, consider another study reported by McDougall, this time from McGill University, showing that gymnasts landing on a mat instinctively adjust their landings based on the thickness and softness of the mat in order to achieve balance upon landing. The same thing happens when we run with cushioned soles: “your legs and feet instinctively come down hard when they sense something squishy underfoot. When you run in cushioned shoes, your feet are pushing through the soles in search of a hard, stable platform.” (p. 173). These adjustments are part of the proprioceptive or “body awareness” sensory system that is built into our neuro-muscular physiology. The story is otherwise when running barefoot on a hard surface:

To see pronation in action, kick off your shoes and run down the driveway. On a hard surface, your feet will briefly unlearn the habits they picked up in shoes and automatically shift to self-defense mode; you’ll find yourself landing on the outside edge of your foot, then gently rolling from little toe to big until your foot is flat. That’s pronation–just a mild, shock-absorbing twist that allows your arch to compress.  (BTW, p. 176)

And according to Dr. George Hartmann, a physical therapist trainer to long-distance runners, pronation is a actually good thing, not the defect it has been made out to be by many:

Your foot’s centerpiece is the arch, the greatest weight-bearing design ever created. The beauty of any arch is the way it gets stronger under stress; the harder you push down, the tighter its parts mesh. No stonemason worth his trowel would ever stick a support under an arch; push up from underneath, and you weaken the whole structure. Buttressing the foot’s arch from all sides is a high-tensile web of twenty-six bones, thirty-three joints, twelve rubbery tendons, and eighteen muscles, all stretching and flexing like an earthquake-resistant suspension bridge…I’ve worked with over a hundred of the best Kenyan runners, and one thing they have in common is marvelous elasticity in their feet. That comes from never running in shoes until you’re seventeen. (BTW, pp. 176-177).

So the explanation here is clear: Our skeletons, musculature and nervous systems are highly refined and well-coordinated adapative systems which adjust both instanteously and by means of longer term adjustments to in order handle the terrain.  These “proprioceptive” adjustments take place virtually beneath the level of consciousness, through the exquisite feedback systems of our body and brain. Try to circumvent these systems, and the protective mechanisms will weaken, exposing us to injury.

I’ve checked this out, and McDougall doesn’t seem to be cherry-picking the research to support his biomechanical thesis.  My informal survey of other research found additional supporting evidence:

• A study by Harvard’s Daniel Lieberman et. al, in the prestigious journal Nature, entitled “Foot strike patterns and collision forces in habitually barefoot versus shod runners“. The study found that “habitually barefoot endurance runners often land on the fore-foot (fore-foot strike) before bringing down the heel, but they sometimes land with a flat foot (mid-foot strike) or, less often, on the heel (rear-foot strike). In contrast, habitually shod runners mostly rear-foot strike, facilitated by the elevated and cushioned heel of the modern running shoe. Kinematic and kinetic analyses show that even on hard surfaces, barefoot runners who fore-foot strike generate smaller collision forces than shod rear-foot strikers. This difference results primarily from a more plantarflexed foot at landing and more ankle compliance during impact, decreasing the effective mass of the body that collides with the ground.”  To see how this works in action, take a look at blogger Karen Given’s interview of Lieberman, who teaches her how to run barefoot and demonstrates how dramatically this reduces the collision forces on her foot and body:
• A review by Warburton in the Australian journal Sportscience, of foot injuries, which found that “Wearers of expensive running shoes that were promoted as correcting pronation or providing more cushioning experienced a greater prevalence of these running-related injuries than wearers of less expensive shoes (Robbins and Gouw, 1991). In another study, expensive athletic shoes accounted for more than twice as many injuries as cheaper shoes, a fact that prompted Robbins and Waked (1997) to suggest that deceptive advertising of athletic footwear (e.g., “cushioning impact”) may represent a public health hazard. Anthony (1987) reported that running shoes should be considered protective devices (from dangerous or painful objects) rather than corrective devices, as their capacity for shock absorption and control of over-pronation is limited. The modern running shoe and footwear generally reduce sensory feedback, apparently without diminishing injury-inducing impact–a process Robbins and Gouw (1991)  described as the “perceptual illusion” of athletic footwear. A resulting false sense of security may contribute to the risk of injury (Robbins and Gouw, 1991).  Yessis (2000, p.122) reasoned that once the natural foot structures are weakened by long-term footwear use, people have to rely on the external support of the footwear, but the support does not match that provided by a well functioning foot.
• Additional studies and commentary, summarized in an article “Should you be running barefoot?” in Runner’s World, by the aptly named Amby Burfoot.  Burfoot’s article has a nice historical overview of great barefoot runners over the past century.
• Barefoot Ken Bob, a somewhat whimsical website devoted to barefoot running as an avocation, which includes research, practical advice, and announcements of upcoming barefoot races.

Finally, here is short video clip that gives a fairly simple explanation of barefoot running technique, featuring aficionado Barefoot Ted, who will be familiar to readers of Born to Run:

This research regarding the adaptive capacity of the foot coheres nicely with the overall thrust of Hormetism, in its confirmation that strengthening of our capabilities proceeds by progressive, periodic exposure to stress, to an appropriate degree and at a rate that allows us to adapt. It may seem paradoxical to some, but the fact remains that our strength is frequently compromised when we resort to crutches or corrective devices in the (misguided) attempt to shield or cushion ourselves from discomforts and shocks.

Technology and paradox. These findings about barefoot running are actually part of a much larger lesson about the paradox of injury, muscular weakening and other adverse consequences that come from an over-reliance on the protective technologies. This larger thesis is in fact the story of a much larger book published originally in 1996 by Edward Tenner: “Why Things Bite Back: Technology and the Revenge of Unintended Consequences“. You might think that a book with that title would be an anti-technology rant. But this book is not that, it is rather an insightful and even amusing look at technology, written by a technophile who does appreciate the benefits of technology, but at the same time was drawn to probe this puzzling downside to our over-reliance on technology. He has pulled together a wide-ranging survey and analysis of what he calls the “revenge effects” of technology, attempting to explain why it is that technologies often backfire in ironic and unexpected ways that tend to undermine their effectiveness. Such a book could go on for volumes if one wanted to catalogue every possible instance of the perverse effects of technology, but Tenner wisely limits his focus to several probing chapters on a handful of especially illuminating fields: medicine, environmental engineering, pest control, the computerized office, and sport. And while he has interesting things to say in all these areas, I would like to pick up specifically on his discussions of sports injuries, which are particularly relevant to generalizing our understanding of the paradox of barefoot running.

Tenner’s discussion covers a wide range of different sports, from high contact sports like boxing, rugby and football, to seemingly benign recreational sports, like running, skiing and tennis.  Football is illustrative of the evolution of a once intensely violent sport. In 1905, a year when there were 23 deaths in intramural collegiate play, President Theodore Roosevelt threatened to ban the sport unless the rules were changed regulating allowable conduct. Later, in 1939, plastic helmets were introduced and after World War II they entirely replaced the thin padded leather helmets used until that point. But this had an unexpected effect:

Where plastic helmets were adopted, players intent on using maximum force to stop an opponent began to use their headgear, with the mouth guard that soon accompanied it, as a battering ram. This intensifying tactic all too often had its own unintended consequence: spinal fracture and paralysis…What seemed to be a technological solution had become an extension of the medical problem…The NCAA banned aggressive use of the helmet in 1976, and injuries dropped…Spearing, the use of a helmet in place of the shoulders to knock down an opponent, is now banned but is still widespread, and not just in professional play.  (WTBB, p. 217)

So protection led to intensification of injury, but this was moderated by additional rule changes. So far, so good. But this reduction in acute injuries was replaced by a more insidious problem, chronic injuries:

While there are fewer catastrophes, most of which result from spearing and other dangerous practices, serious injuries have actually increased with the spread of better protective equipment. From the First World War through the 1950s, only four in ten professional players per season reported injuries that needed surgery or resulted in prolonged absence from the game. By the 1980s, seven in ten were seriously hurt each season, according to a study by the NFL Players Association…The game’s “ballistic” style calls for brief but powerful bursts expressed as joint- and vertebra-jarring collisions far more severe than those of Theodore Roosevelt’s day. The helmets, face shields, mouthpieces, and padding are better than ever, and deaths may be rare, but neither protective nor conditioning technology can prevent damage to the joints. Since massive injections of anti-inflammatory drugs and painkillers make it possible for battered athletes to return to play, the new intensity means trading immediate relief for long-term disability…Knee and hip surgery can extend players careers, but usually only at the price of later pain, inflammation, and repeated rounds of surgery. (WTBB, pp. 218-219)

Football is certainly not unique in this regard.  For example, Tenner makes a similar points about skiing:

The replacement of wood by plastics and composites in the 1950s changed and extended the sport just as dramatically as lifts had done earlier in the century. Gone were the rituals of waxing. And on the way out, it seemed at the time, were the broken bones that once formed part of the folklore of skiing. At first, the new equipment shifted some of the injury from ankle fractures (common with lower prewar boots) to twisting fractures of the tibia. A fall often led to this spiral break of the bone. Then came further improvements. New, rigid plastic boots and bindings employing strong, lightweight alloys were designed to release the legs of skiers at a predetermined level of force…To the extent that skiers are risk seekers, they will respond to safer equipment and more carefully maintained slopes by seeking more dangerous runs and increasing their speed….Protection also leads to greater risk-taking in the slalom event, where skiers voluntarily use protective gear, including helmets, to take a straighter course down the slope…In the days of wooden skiis, the cast-encased leg was a cartoonist’s cliche, but with some reason….ACL sprains now account for up to six injuries a day at large resorts and up to 100,000 annually in the United States. Surgeons can usually repair a torn MCL by stitching ends together: a sprained ACL demands much more difficult techniques, including tendon grafts. (WTBB, p. 224).

The basic message in all of the above is that as protections have increased, injuries have not gone away, but have shifted from the acute to the chronic, and in many cases chronic injuries that are more enduring and difficult to deal with. This message is consistent with the point made on the Rehabilitation page of this blog about the downside of “crutches” such as canes, orthodics, and even eyeglasses.  The difference, in this case, is that these protective aids defeat our intentions in a different context than that of rehabilitation. Instead of impairing our recovery from disability, these protective aids instead make us vulnerable to injury.  (While the distinction between prevention and recovery is important, there is actually the interesting case of Michael Sandler whose RunBare blog documents his story of how he used barefoot running to overcome a serious shattered leg injury, transforming himself from being unable to walk, to running barefoot 80-100 miles per week!)

Protections such as extra support or cushioning no doubt make us safer in certain respects. But while guarding against the strong shocks that can cause acute injury, these very protections can mask the sensory inputs that our body uses to adjust and adapt internally–both in the instant and over time. In doing so, we are making ourselves vulnerable to repetitive stress or other low level chronic injuries that, over time, can become at least as serious, if not more so, than acute injures, because the healing process is not as straightforward.

Lessons. So where does this leave us, and what should we do about it?  Should we always run barefoot and forgo all the protections of padding and modern protective technology when we engage in challenging physical activities like sports? I certainly would not advocate that. But I think the key point here is to be conscious of what we give up by relying on artificial external protections, especially if it means decreasing our reliance on our own internal musculature and nervous system.  We should be wary of getting too far away from contact with our raw senses and physical exertions whenever we pick up a piece of protective athletic equipment, clothing or footwear, and we might consider how to make internal strengthening and perceptual sharpening an essential part of our conditioning when we train and prepare for athletic performance or even to enhance our ability to navigate the ordinary physical challenges of daily life, such as climbing stairs, or lifting groceries or children. In short: beware of “labor saving” devices; the labor you end up saving may actually be have been useful or necessary to your well being!

What do you think?  Please leave your comments below, or visit the Discussion Forum.

Biological markers. After these ordeals, Dr. Andy Morgan of Yale Medical School found that the top performers had very different physiological responses from those who couldn’t hack it. He did extensive physiological monitoring and found that those who passed these tough tests had much higher levels of NPY (a neuropeptide) and DHEA (a hormone that buffers the effects of cortisol, a stress hormone).  In addition, those who did best also had “metronomic heartbeats” — very little heart rate variability (HRV), compared to most normal people, who show a lot of variability in the intervals between heartbeats.

These biological markers of stress-resistant individuals show that they are somehow different than most of us.  Perhaps this is worth looking for what it can teach the rest of us.   Certainly, there are other health known health benefits that have been reported for NPY and DHEA.

Autonomic nervous system. Regarding HRV, however, Sherwood raises a caveat, noting that numerous studies have associated metronomic heartbeats (low HRV) with cardiovascular disease, diabetes, and even sudden death.  However, other research into the HRV paints a more complex picture.  A paper on the Intellewave Method,  by Dr. Alexander Riftine,  indicates that low HRV may have different implications for the state of the autonomic nervous system, depending on the frequency of the heartbeat variability, derived from heart rhythmograms.  When spectral analysis (a mathematical technique based upon Fourier Transforms) is applied to the heart rhythmograms, the heartbeat frequency variations are resolved into high frequency (HF) and low frequency (LF) patterns.  The LF variations are associated with the sympathetic nervous system (SNS), where as high frequency HF variation correlate with the parasympathetic nerous system (PSNS).  The balance between SNS and PSNS states predicts much about an individual’s fitness.  According to Dr. Riftine, these states cluster into nine typical combinations.  The ninth state–an elevated PSNS with a reduced SNS state–is “rather unusual because normally an increase in PSNS is accompanied by an increase in SNS.  This rare condition is found in water polo athletes, long-distance runners, navy seals and persons with special heart training for deep sea diving.”

The physiological analysis of individuals who have successfully adapted to tolerate stress is a promising area ripe with lessons for the rest of us, as it could be used to assess, predict, and track our progress in getting stronger and more stress-hardy.

Tennis. Loehr gleaned some of his most perceptive insights by using telemetry to observe the behaviors that separated the top tennis players from the lower ranks. Specifically, he found that the best tennis players are intense and focused during play, but show a remarkable ability to recover during “between-point” time, following routines that allowed them to pause and recover their energy for the next point. During these brief periods–approximately 25 seconds–between points, “top competitors were much more skillful oscillators during competition. The rhythmic increases in heart rate during points, and decreases in heart rate between points, meant that a competitor was adapting to the stress.” (SFS, p. 167). By contrast, poor competitors did not use their downtime wisely, not relaxing or even exacerbating the stress by disputing calls or showing emotion.

Toughening. The best of Loehr’s ideas are encapsulated in Part III of “Stress for Success”, entitled “Life Skills and the Toughening Process: Targeting Stress Exposure”. This section presents what I believe are the key concepts for effective toughness training based upon deliberate and controlled exposure to stress. Loehr takes research from sport science and applies it to training for toughness in everyday life.  ”For decades, sport science researchers have been diligently investigating the relationships between stress and growth.  The optimal frequency, duration, and intensity of stress exposure for improving strength, speed agility, endurance, stamina, and toughness of all kinds have been vigorously pursued. The most important confirmation in all the research is simple and direct:  STRESS IS THE STIMULUS FOR ALL GROWTH.”  (SFS, P. 145).

Oscillation. Loehr goes on to describe training routines whereby one can increase stress tolerance by deliberately using intermittent intervals of stress exposure, oscillating with periods of recovery and rest. One of the most effect means of doing this is excercise, specifically interval training. According to Loehr, “exercise is really stress practice,” and he cites the training principle of “specificity” to argue that the exercise stress should oscillate, so that they resemble the up-and-down of stresses in real life. The intermittent stresses should be intense to the point of discomfort, but never painful. And the use of intervening periods of “active rest” and sleep are equally important for recharging.

The benefits of this approach to oscillatory stress training have biochemical correlates. Loehr cites research indicating that, whereas chronic, sustained stress leads to depletion of the stress hormone norepinephrine and elevation of cortisol, intermittent acute stress, followed by recovery, allows for increased tolerance and resistance to norepinephrine depletion.

Although Loehr mentions that sports scientists have studied the optimum intensity, duration, and frequency of applied stresses in exercise, he does not provide in his book any specific guidelines for optimizing these variables, beyond noting that they will vary based on the nature of the stress and subjective factors such as discomfort and pain thresholds. While being aware of one’s own thresholds is no doubt good advice, it seems to me that turning exploring the quantitative aspects of this science would be useful in helping to reveal more objective factors.

Beyond exercise. I believe that the application of stress and recovery cycles for training can be generalized beyond the use of physical exercise. Following the principle of specificity, why not train for life using more  specific stresses encountered in life, specific distractions or irritants, including physical stresses such noise, heat, or hunger; or interpersonal irritants such as yelling, nagging, or insulting. In fact, such deliberate exposure to stress and hardship is a techniques going back to the Stoics, who recommended training oneself to tolerate increasing levels of physical stress and discomfort by means of cold baths, sleeping on the floor, fasting, and learning to tolerate insults. Extreme forms of such exposures to stress have been used by the Army and Navy to harden their special forces (See the post on Stress Inoculation), but I believe there is a lot of opportunity for both creativity and the use of proven behavioral science in developing and optimizing specific and effective techniques to help us become more resistant to a variety of life’s everyday stresses.