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morendurff83
03-23-2010, 06:24 AM
Dear Subscribers,

Nature is to be congratulated for publishing confirmatory work (Liberman, DE, et al, Nature, 2010 463:531-535) that the biomechanics field published more than 20 years ago (Robbins SE, Hanna AM. Med Sci Sports Exerc 1987 Apr;19(2):148-56) concerning barefoot versus shod running. However, the conclusions of both studies remain highly speculative and controversial, highlighting the need for well-controlled randomized clinical trials of barefoot vs. shod running adaptations before meaningful conclusions can be drawn.

Running related injuries are diverse, suggesting several different injurious factors for specific individuals. Injuries from habitual endurance running span the full range of bones, joints, tendons and muscles from toes to spine, suggesting that running stresses the entire organism and any one of many different components may be injured. In general I agree that loading rate might be important, but the loading rate of muscles, tendons, ligaments and bones is much more related to injury than ground reaction force loading rate. The metric of interest is not the forces applied to the ground, but the frequency content, amplitude and number of impact transients transmitted to specific anatomic structures over time. Most running injuries are chronic but a few are acute.

The primary injuries from barefoot running might be plantar puncture, abrasion and laceration wounds, plantar bruising, stress fractures of the metatarsals and Achilles tendonitis/tendonosis. We decided to build shoes for a reason—pain relief. Modern cushioned shoes despite all their hype and expense and fashionable colors protect the body by reducing the high frequency content of these transients, regardless of the foot contact pattern. They are not perfect, but they are reasonably effective.

Liberman argues that the stiffened soles and arch supports in running shoes may weaken the intrinsic musculature of the foot. “Furthermore, many running shoes have arch supports and stiffened soles that may lead to weaker foot muscles, reducing arch strength. This weakness contributes to excessive pronation and places greater demands on the plantar fascia, which may cause plantar fasciitis."

This statement suggests that all runners who wear shoes would eventually become pronated, which is hardly the case; many have varus and/or cavus and this does not resolve with running, either shod or barefoot. Liberman is suggesting the mechanism of the increased load on the plantar fascia makes it weaker. Why does wearing shoes make the post tib weaker? Why would post tib weakness lead to plantar fascia weakness (midfoot torsion?!) more than the very high forefoot bending moments that forefoot contact running elicits? Wouldn't barefoot (forefoot) running load the plantar fascia much more than shod running? Is this loading a good thing or a bad thing? Weaker or stronger? It depends on dose (magnitude, duration, frequency, mode, training history, nutrition…).

Barefoot endurance running is not likely to increase the strength of these muscles as effectively a performing three sets of 20 plantarflexion motions barefoot—muscle hypertrophy is best achieved by high-load, low repetition movements that trigger mTOR molecular signaling cascades that result in increased contractile protein synthesis. These hypertrophic mechanisms are partially blocked by TSC2 which is activated during endurance exercise through the AMPK pathway that results in increased fat metabolizing enzymes (Coffey, et al, 2005, 2009).

This suggests that “weight training” barefoot might be effective in strengthening the intrinsic musculature of the foot. Performing an endurance activity to gain strength is something like that quote by Mao about fighting for peace…

I would wager that the windlass effect places much higher forces (and excursion) on the plantar fascia and that MP extension (forefoot flexibility) is key, but that limited high-force events should be undertaken for novice barefoot runners, especially at first.

It is exceeding unlikely that endurance running as is currently practiced by modern humans is anything like our prehistoric hunting practices. Anyone who has attempted persistence hunting of large game on foot will quickly realize that they have horns for a reason: if the initial flush to initiate running in these animals is successful, additional attempts are often met with charging behavior and panicked sprinting by the hominids in all directions to avoid a “Pamplona”-type injury.

Having hunted antelope with Africans using a bow and arrow I know this scenario to be plausible. Our forbearers supposedly hunted like this with nothing more than long, sharp sticks. There is something valuable in living one’s hypotheses that makes a charred (steer) steak and a cold beer taste all the better around the fire after total failure. It may be our ability to excel at endurance running that initially set us apart from other organisms, but it is our ability to ask why that sets us apart now.

It is much more likely that this persistence hunting activity should be described as high-intensity intermittent exercise (HIIE) which persists for long periods at varying intensity levels. For human musculoskeletal health these HIIE activities resulted in a balance between endurance capacity and overall musculoskeletal strength. The foot and ankle would have received a wide array for force-time stimuli resulting in a joint complex that would be resistant to fatigue and injury, and yet perform at a very high level.

This is an interesting debate, but I hardly think the main thrust of our efforts should be to help habitual runners run even more. Our efforts would have a much bigger health and economic impact if we worked to make habitually inactive people active. For example HIIE activities like football (soccer) have been shown to be much more effective than running at providing a training effect in previously sedentary individuals (Bangsbo, et al, 2009), reducing fracture risk (Helge, et al, 2010) and reducing coronary risk factors in women (Andersen, et al, 2010) and men (Krustrup, et al, 2010), increasing musculoskeletal strength and balance (Sundstrup, et al, 2010), endurance and well-being (Krustrup, et al, 2010) and reducing hypertension and coronary risk factors (Andersen, et al 2010). Soccer players have much higher bone mineral density at their spine, femur and tibia compared with runners (Fredericson, et al, 2007) and adults who played ball sports as children have fewer stress fractures as adults, even when training for national running competitions (Fredericson, 2005).

Forget barefoot running—play soccer instead.

Michael Orendurff
Division Director
Movement Science Laboratory
Texas Scottish Rite Hospital for Children
Dallas



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