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A comparison of the biomechanics and injury profile of running shod and barefoot

To run barefoot or in training shoes?

Introduction
Historically athletes were barefoot in the sporting arena and it is only a relatively recent phenomenon for shoes to be worn in competition. In Roman times wrestlers competed barefoot, whilst runners wore little more than thin leather sandals to compete over long distances. More recently several athletes have achieved significant success competing barefoot: Abebe Bikila from Ethiopia won the Rome Olympic marathon in 1960, and Zola Budd became the world record holder over 5000 meters. Since the 1970’s athletic shoe manufacture has boomed and with it so too has the incidence of running-related lower limb injuries. This prompted the question of whether these new designs were to blame for the injuries or simply reflected the growing interest in distance running as a sport. That notwithstanding, the interest around barefoot running to reduce such injuries has grown exponentially. This account aims to appraise some of the literature on this contentious subject.
 
Background
Gait cycle and running biomechanics The normal gait cycle consists of both stance and swing phases. The stance phase occupies 60% and swing 40% of the time taken to complete one cycle of consecutive heel striking by the same foot. The stance phase itself is divided into contact, midstance and propulsive phases. It begins and ends with both feet in contact with the ground known as the ‘double support phase’. The swing phase is divided into follow-through, forward swing and foot descent phases. The phases of running are very similar except for the fact that there is a flight phase when neither foot is in contact with the ground between stance phases. Evidently, with slower jogging the stance phase is longer than the flight phase, however, during sprinting this relationship reverses and the stance phase becomes the shorter of the two phases.
There are several key biomechanical considerations that must be borne in mind before a comparison can be made between barefoot and shod running. During running there is an increase in rotation at the pelvis, hip, and knee which must be absorbed by increasing the muscle forces acting over these joints. Moreover, as running speed increases the point of foot impact changes from predominantly heelstriking to that of forefoot weight-bearing when sprinting. The normal angle of gait is approximately 100 abducted from the line of progression. As speed increases this angle decreases approaching zero as the foot strike nears the line of progression. Runners who have developed stride patterns that incorporate low levels of impact force and rapid pronation are at a reduced risk for over-use running injuries such as stress fractures, plantar fasciitis, and  ligamentous sprains. It is important to note that many shod runners never develop injuries, however, the available data indicates that 19-79% will develop an injury over  their years spent running.

1. Biomechanical abnormalities and injury
1. Excessive Pronation – Pronation of the foot occurs at the sub-talar joint and when it occurs in excess is associated with many running-related injuries. Examples include, first metatarsophalangeal joint abnormalities, medial arch and plantar fascia strain, Achilles and tibialisposterior tendinopathy, patellofemoral joint dysfunction, and stress fractures. One study illustrated that shod running decreased torsion and increased pronation significantly, the paper concluded that the reduction in torsion produced by stiff soled shoes may well be a factor in running injuries caused by excessive pronation.

2. Excessive Supination
This movement also occurs at the subtalar joint and may compensate for a weakness of the antagonist pronating musculature (e.g. peroneal) or as a result of spasm or tightness of the supinating musculature (e.g. tibialis posterior, and the gastrocnemius- soleus complex). The supinated foot is less mobile and provides inferior shock-absorption which may well predispose to the development of stress fractures of the tibia, fibula, calcaneus and metatarsals. Lateral instability of the foot and ankle may be associated with excessive supination resulting in an increase incidence of ligamentous sprains of the foot and ankle. Such a lateral stress on the lower limb could result in tightening of the ileo-tibial band with associated bursitis of the femoral epicondyle.

3. Abnormal pelvic mechanics
During normal running the pelvis assumes a rotated position with anterior-posterior and lateral tilt. Weakness in the muscles needed for stabilisation of this position will result in excessive movement in any one of the three planes. A less efficient transfer of force will subsequently occur. The most common pelvic abnormalities are excessive anterior tilt, excessive lateral tilt and asymetrical pelvic movement. The complex inter-play of musculature to compensate for each of these abnormalities may well result in muscle tightness, strains and tendinopathy. Adaptation and biomechanics of running barefoot A leading study on the subject of barefoot running was conducted by Lieberman et al. who compared foot striking patterns and collision forces in habitually barefoot with shod runners. They found that habitually barefoot endurance runners often land on the fore-foot (fore-foot strike) before bringing down the heel. Less frequently they may also land with a flat foot (mid-foot strike), or even less often, on the heel (rear-foot strike). In contrast, shod runners mostly rear-foot strike which is facilitated by the elevated and cushioned heel of the modern running shoe.
The same study conducted kinematic and kinetic analyses on the two populations and discovered that even on hard surfaces, barefoot runners who fore-foot strike generate smaller collision forces than shod rear-foot strikers. This is brought about by the manner in which the barefoot runner’s foot is more plantarflexed at landing with a greater degree of ankle compliance at impact. These features combine to decrease the effective mass of the body that collides with the ground and so potentially reducing
injury through repeated heavy loading. In addition, the stride length of barefoot runners is shorter and the strides have a greater vertical leg compliance which acts to
lower the body’s centre of mass relative to the force of impact[7]. Again, these features work to reduce jarring and result in a smoother running motion experienced by the individual.

Footwear and Injury:
It has been surmised that modern footwear produces a lower level of perceived foot impact than that actually experienced and thus increases injury risk. There is good  evidence to show that the more cushioning runners believe to be under the foot, the harder they strike. Furthermore, modern shoe designs are far more forgiving on poor running technique and since the athlete suffers less pain bad habits become re-inforced. In contrast, barefoot runners have been found to have a reduction in impact peak with reduced mechanical stress and enhanced ankle extensor function. In one particular study peak load in the hip and knee joints of participants with osteoarthritis was decreased significantly in barefoot walkers. These findings appear to point to the supposition that shoes may increase loads in poor physiological patterns and thus perpetuate injury.

Conclusion:
Bipedalism has been around for millions of years and it is only relatively very recently that humans have been shod. The running technique of early distance running bipeds almost certainly differed enormously from the style that is seen today with modern foot-wear. The pre-historic ‘hunter-gatherer’ would be more likely to have had a fore-foot or mid-foot-strike gait which studies have shown to be protective from many of the running injuries seen today.
Modern running shoes allow a greater degree of ‘laziness’ in running style and in so doing ingrain bad habits which ultimately predispose to injury. Information on how barefoot running can be integrated into one’s training and how to overcome the obvious hazards of penetrating and friction injuries are growing at a great rate through internet forums and sites. There are already products available such as the Vibram FiveFingers® which are gaining in
popularity as the option of running barefoot or ‘nearly barefoot’ grows. Furthermore, interest in the subject has been helped enormously by popular literature such as the bestselling book ‘Born to Run’ by Christopher McDougall[11] which follows the Tarahumara Indians of Northern Mexico who run ultra-marathons in simple leather strapped sandals. In short, the evidence indicates two clear points. Firstly, from observations of populations who run barefoot or are habitually barefoot there appears to be lower
injury rates versus the shod population[12]. Secondly, the wearing of modern running shoes promotes a heavy impacting heelstrike gait which predisposes to injury. For
the subject to gain wide-spread acceptance there will need to be an increase in the number of well designed prospective and randomised controlled trials on the subject.

References:
1. Clinical Sports Medicine by Peter Brukner and Karim Khan. Third Edition, Chapter 3; pp.45-55
2. Hreljac A. Impact and overuse injuries in runners.
Med Sci Sports Exerc 2004; 36:845-9 3. van Gent RN, Siem D, van Middelkoop M, van Os AG, Bierma-Zeinstra SM, Koes BW. Incidence and
determinants of lower extremity running injuries in long distance runners: a systematic review. Br J Sports Med 2007; 41(8):469-80
4. Buschbacher R, Prahlow N, Dave SJ (eds). Sports Medicine and Rehabilitation: A Sports Specific
Approac, 2nd ed. Baltimore (MD): Lippincott Williams and Wilkins; 2008, p. 200-1
5. Stacoff A, Kaelin X, Stuessi, Segesser B. The torsion of the foot in running. Int J Biomech 1989; 5:375-89
6. Lieberman DE, Venkadesan M, Werbel WA, Daoud AI, D-Andrea S, Davis IS, Mang-Eni RO, Pitsiladis Y. Foot strike patterns and collision forces in the
habitually barefoot versus shod runners. Nature 2010; 463:531-535 7. Jungers WL. Barefoot running strikes back. Nature
2010; 463:433-434 8. Robbins S, Waked E. Hazard of deceptive advertising of athletic footwear. Br J Sports Med
1997; 31(4):299-303. 9. Divert C, Mornieux G, BaurH, et al. Mechanical comparison of barefoot and shod running. Int J
Sports Med 2005; 26:593-8 10. Shakoor N, Block JA. Walking barefoot decreases loading on the lower extremity joints in knee
osteoarthritis. Arthritis Rheum 2006; 54:2923-7 11. Christopher McDougall. Born to run: the hidden
tribe, the ultra-runners and the greatest race the world has never seen. Profile books, published 2009.
12. Robbins SE, Hanna AM. Running-related injury prevention through barefoot adaptations. Med Sci Sports Exerc 1987.;19:148-56

A comparison of the biomechanics and injury profile of running shod and barefoot