Barefoot running causes a lower risk of injury and increases performance compared to shod running
By Mark Zureik
Key Words
Barefoot, Shod, Gait, Biomechanics, Running
Abstract
Background: Barefoot running has been gaining a following in the endurance running community over the last decade. This has been attributed to the success of some barefoot runners in competition who, despite popular belief, have found greater success when running barefoot rather than running shod. This transition from habitually shod to barefoot has confounded biomechanists due to the belief that the traditionally barefoot runners (Kenyans) were born into their running method and that the shoe was superior. Current studies are attempting to discern the differences between shod and barefoot running and the efficacy of this practice. On top of this, commercial companies have began producing footwear that helps mimic a barefoot style but the efficacy of such footwear is yet to be proven . This literature review aims to examine the current body of evidence for the efficacy of barefoot running in decreasing the risk of injury and increasing performance compared to their shod counterpart. Also the issue of whether new model minimalist shoes can mimic barefoot running adaptations is addressed.
Method: Databases such as MEDLINE, Sport discuss, AUSPORT, Cochrane library, Web of Science and Scopus were searched for any relevant studies. Studies were analysed for careful collection of data and most importantly if there is any outside bias that may have affected the results of the study (which has been discovered on occasion).
Results: Barefoot running results in lower ground reaction forces which are better tolerated due to adaptations that occur such as increased muscular activation, gait changes and increased joint movement. Thus, barefoot running appears to be a more suitable biomechanical modality for preventing injuries and increasing performance compared to shod running when the user is acclimated and practiced. More high quality studies need to be performed before this method of running can be recommended as the preferred method of running.
Conclusion: This review would suggest that barefoot running could be a better form of running to decrease the risk of injury and increase performance in perfectly healthy experienced runners. The use of minimalist shoes to mimic a barefoot style of running is worthwhile as it provides the similar benefits of barefoot running with more protection. As for whether barefoot running is superior for people with certain conditions or fitting particular demographics, such as low arch’s, will require much more research to be undertaken.
Introduction
Since the beginning of civilisation humans have traditionally run barefoot or in minimalist shoes. The modern day running shoe is a complex design consisting of an insole, cushioned heel, contoured for the foot arch’s, copious lacing and light material which is in stark contrast to the leather sandals or animal skin shoes of old. [1] [2]
Recently a resurgence has occurred in the running community for the adoption of a free, barefoot style of running that utilises a “natural”, inherent way of running. This resurgence can be attributed to the successful utilisation of barefoot running by, at first, runners that were raised in a barefoot style (African runners such as Abebe Bikila) and then the conversion of shod runners to barefoot.
Barefoot running produces a lower rate of injury compared to shod running due to a couple of adaptive mechanisms that only occurs in the barefoot condition [3]. This is attributed to the different biomechanics of barefoot runners which is the evolutionary preferred method for bipedal homosapiens [4]
Gait is the way humans move from one place to another which involves both walking and running. Gait is comprised of 2 phases – A stance phase (60%) and a swing phase (40%). Each of these 2 phases is comprised of different components (listed chronologically) which are Heel Strike, Flat Foot, Mid-Stance, Terminal Stance and Toe off in stance phase; followed by initial, mid and terminal swing in swing phase.
In barefoot and shod conditions, there are marked differences in the temporo-spatial and kinematic features of gait because of a variation in how these conditions achieve locomotion [5]. A general description of shod walking/running is an outward heel strike that travels towards the big toe while the opposite occurs in barefoot where the lateral ball of the foot will strike initially, then heel contact and lastly toe off at the big toe [6].
Kinetic data concerning forces and torques have been measured and compared in the shod and barefoot conditions. A most important measure is the Ground Reaction Force which is the force returned through the leg beginning at heel strike (or fore foot strike). There are 3 vectors though which these Ground reaction forces occur – vertically (directly upwards), medio-lateral (side-to-side) and lastly anterior-posterior (acting forward and backwards). Measurement of ground reaction forces, torque about the ankle/knee and foot strike patterns are common features in many studies analysing barefoot and/or shod running conditions. Generally these forces are 300% lower in barefoot runners then in shod runners and load at a 700% slower rate [7]. Torque is the rotational force that that occurs during gait around the joints of the foot, ankle, knee and hip. This torque production is a mechanism of energy transfer that occurs up the kinetic chain and helps equally distribute force [8]. Torque and force analyses are extremely important in understanding the quantitative differences between barefoot and shod running conditions.
The resurgence of barefoot running has also concurrently brought about the creation of shoe’s that cater towards this market. The most popular being the Vibram 5 fingers which have increased sales since they came on the market in 2006 to a record $11 million in sales in 2010.
Kinematic comparison of barefoot and shod running
The most obvious feature that differentiates properly trained barefoot runners and shod runners is the difference in gait patterns. The initial strike which is at the heel in the shod runner and in the fore or mid foot for the barefoot runner is the main difference
It is well established that the arch’s and other soft tissues of the foot provide elastic energy that assists in gait [9] [10]. Proponents of barefoot running claim that the fore foot running gait improves the ability of the foot to dissipate energy as it is a more efficient use of the foot arches. The mechanics of a fore foot strike allows the longitudinal arch of the foot to lengthen as the foot drops and then shorten effectively as the foot is raised and also dissipates energy through the rotation at the ankle [7]. In rear foot striking the action of the lateral heel strike to a medial big toe toe-off causes the foot and ankle to deal with preventing over pronation rather than energy economy. Comparatively barefoot runners have the least pronation compared to their shod counterparts [11] . This pronation, if excessive, is generally treated with foot orthotics very effectively [12].
In barefoot gait, the ankle lands at a more plantar orientation then in shod conditions – this accounts for the inherent need to land in a fore foot action rather than rear foot [13] [14]. Stiffness also increased with the use of running shoes, helping to explain the lower amount of ankle rotation during shod running [14]. It is worth a mention that in the previous study only higher cushioned shoes had a significant stiffness difference, supporting the use for low cushioning shoes to mimic barefoot running. Joint stiffness increases as a way to deal with increased force through the joint [15].
These adaptations that occur in barefoot running are thought to be neurophysiological in nature and an inherent necessary alteration to being able to run barefoot[16] . It would be impossible to heel strike in a barefoot condition as this causes a maximum deformation of the heel pad which is greatly attenuated by the modern running shoe – barefoot heel deformation was maximum but lowered by 45% in running shoes[17]. Of course this issue is entirely avoided in forefoot striking as the body weight rotates downward in a fore foot strike as the heel travels to the ground whereas in a heel strike the entire weight is placed on the heel pad and only the forefoot rotates towards the ground.
An experimental fault to consider in kinematic analysis is that the skin markers used are somewhat unreliable as they can over estimate skeletal movements since they are skin mounted [18]. Intracorticol bone markers have been used as a more reliable, but more invasive, alternative [19].
Figure 1. A summary of the main kinematic differences in barefoot and shod running
Kinetic comparison of barefoot and shod running
When discussing kinetics in gait we are looking at forces and torques that occur around the lower body. Numerous studies find that barefoot running leads to an overall lower amount of impact forces generated than their shod counter parts, varying between 50% and 300% lower [7, 20, 21] [22].
Barefoot runners had a lower braking force but a higher pushing force and a higher (but more temporally spread) medio-lateral force [16]. This longer period of loading assists the foot structures to deal with this force and may be a possible reason why pronation is lower in barefoot runners.
Shoe wearers had a higher amount of joint torques at the ankle, knee and hip which is associated with increased risk of osteoarthritis development [23]. This overall lower amount of forces and torques is what lends the barefoot runner to being less injury prone but this observation has yet to be fully established in literature.
However there is evidence which demonstrated shoes as superior. Shod running was found to be superior to barefoot as it produced lower force propagation because of the presence of a cushioned heel[24]. As previously mentioned heel striking with a bare foot will result in injury and it is the writer’s opinion (and not mentioned in the study) that the participants were not educated on proper technique. This paper was also presented at a symposium which was funded by Nike and Adidas (popular sport shoe companies) which may have influenced results.
Figure 2. A summary of the main kinetic differences in barefoot and shod running
Muscular Activation (EMG) comparison of barefoot and shod running
Muscular activation changes are also different in the two conditions. An increased activation of lower leg muscles indicated by EMG during gait causes a better damping effect of energy [25] . Barefoot running does induce an increased muscular activation of the lower leg musculature of up to 10% differences in various muscle groups (in peak values and pre-activation levels) [26] [27]. Increased EMG signals correspond to increased strength gains [28]
Pre-activation levels also increase in barefoot running compared to shod running [20]. It is normal to see an anticipatory increase in muscle EMG in preparation for the initial contact of the foot so as to shunt the ground reaction forces from passive (bones, ligaments, and fascia) to active (muscle) components which can absorb these force’s and face no risk of plastic changes. It has been suggested that the lower proprioceptive ability of the plantar foot in shod running could play a role in lowering muscular activation [29]
An aspect that the current EMG research fails to address is the anecdotal improvement in the intrinsic muscular of the foot in terms of function (various components form muscular function – strength, cross sectional size, motor unit firing, motor unit efficiency, fatigue resistance, innervation strength etc..) – This is where barefoot running advocates claim how barefoot running is partially more natural and better able to prevent injury (increased muscular function causes a decrease in dysfunction related injuries).
| Barefoot | Shod | ||
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Increased muscular pre-activation levels(pre-activation that occurs before striking the ground). Higher peak EMG indicating higher muscle activity during the stance phases
Hypothetically increased muscularstrength from this adaptation |
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Lower EMG of pre-activation and peak activation of lower leg musculature Shoe possibly attenuates feedback mechanisms of motor unit activation and recruitment via stimulation of cutaneous receptors |
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Figure 3. Summary of Muscle adaptations and activity
Efficacy of minimalist/free footwear
Athletic shoes are a multibillion dollar industry across the world. Barefoot running threatens this market domination as it attacks the foundations on which these shoes are based on – that they are essential to any running activity. This also raises the issue of certain influencing factors that may “skew” results of particular studies on a new type of foot wear that wasn’t initially sold by the big companies – minimalist footwear. Shoe’s that offer little to no arch support or even just material to protect the foot have become a popular item to purchase. Vibram recorded $11 million in sales of their brand of shoes with expectations to rise over the next coming years.
Wearing shoes increases the energy cost of running. As shoes & orthotics are added to the runner, a higher amount of oxygen is consumed for the same speed and workload compared to barefoot runners. The difference was a 1-3% increase in oxygen consumption, with higher effects for heavier shoes [30].
Minimalist foot wear use for 5 months caused an increased strength gain of between 4 and 10% of the flexor digitorum longus, abductor hallicus, quadratus plantae, and Abductor digiti minimi and flexor hallicus longus by using Nike Free shoes [27]. This increase in strength compared to regular running shoes demonstrates the increased workload in which these muscles had to adapt to – and thus it is a safe assumption to conclude that similar mechanisms are employed in using this footwear as in barefoot running[27] . This supports the efficacy of the use of minimalist or free foot to mimic the advantages of barefoot running
The use of Vibram’s was able to mimic a barefoot style of running and in fact improved the energy efficiency of barefoot runners. A similar strike pattern was noted in the Vibram’s as in barefoot runners [6]. Vibram’s were superior to both normal shoes and barefoot running – the former because of a weight difference of 400g and the later due to the vibram offering just enough support to actually help rather than hinder motion at the foot joints. This physiological superiority of minimal/barefoot running causing a 3-4% decrease in O2 consumption and energy expenditure was also found in other studies [31].
The use of minimalist shoes does provide the same performance benefits that barefoot running and can be worn by those interested in taking up the practice. More high quality studies need to be performed that can further prove the superiority of these minimalist shoes over the traditional running shoe which has substantially more proof to back its efficacy.
Conclusion
Barefoot running appears to be a highly viable running recommendation in the near future if research continues to be favourable. The main issue now is that while the research points towards barefoot running as a means to prevent injury and increase performance it has to overcome decades and a plethora of high quality scientific evidence that supports the use of orthotics and shoes in runners who traditionally have run with a rear foot stance.
Some future directions are definitely needed to legitimize this practice.
- Overall more high quality studies need to be performed to create a base of quality, peer reviewed data.
- Certain issues need to be addressed – barefoot running may be great in the serious athlete who has practiced it but what about the casual runner? What about those with biomechanical problems that are addressed with shoes/orthotics such as high and low arch’s
- Technique needs to be perfected to specific gait modifications and not just basic recommendations that are given today.
Summary points
- Barefoot running causes gait changes that lend towards a less impacting running style
- Barefoot runners have a higher EMG (both pre-strike levels and during contact) of the leg muscles which dampens the effect of striking the ground
- The ankle moves more in barefoot running due to lower joint stiffness. Joint stiffness is related to force that translates through it
- Overall forces are lower in barefoot conditions and are better able to be managed in a fore foot strike
- Barefoot or minimalist shoes provide a slight performance boost because of the lack of shoe weighing. Minimalist shoes are able to mimic a barefoot running gait.
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