THE EFFECT OF CONVENTIONAL RUNNING SHOES ON THE FOOT AND THE BENEFITS OF MINIMALIST FOOTWEAR
Blaming the running injury epidemic on big, bad Nike seems too easy – but that’s okay, because it’s largely their fault.
It was usually only seen within the alternative circles of society and the occasional Olympic athlete; however since the release of the award winning book ‘Born to Run’ by Christopher McDougall, the trend and appeal of barefoot running has grown exponentially. The rise of the ‘barefoot movement’ has sparked criticism and applause amongst different groups, with mixed reviews and a burden of proof over its legitimacy.
The criticism of the barefoot movement stems from the sole idea that there is insufficient evidence to prove the benefits and that there is no research into the long-term effects of barefoot running; with the implication and attitude that the long-term effects are potentially harmful.
This essay will examine the evolution of the human foot, the history of running and the development of the modern running shoe. The implications of the running shoe will be highlighted by analysing the varying running styles, injuries and other health effects. To conclude, the essay will examine the rise of minimalist footwear and the benefits they posses.
EVOLUTION AND RUNNING
As a species we are designed to endurance-run barefoot. The human foot evolved approximately 270 million years ago (Haines, 1999), and it is noted that we evolved over millions of years running long distances to survive (Bramble & Lieberman , 2004) (Lieberman & Bramble , 2007). Most predator or prey mammals use speed and agility to survive, unfortunately due to the biology of most mammals their ability to maintain survival speeds for more than a few minutes is hampered by a choice; they can either keep running, resulting in overheating and death, or they can stop and cool down – they cannot do both (Krabak, Hoffman, Millet, & Chimes, 2011, p. 1143).
The estimated human running speed is between four and six metres per second, faster than the average speed a non-human mammal can transition from trotting to galloping. This factor, along with the human body’s unique ability to cool down through perspiration, allowed our species to outlast any other mammal on the savannah, literally running them to death; all of this was achieved without the conventional running shoe (Krabak, Hoffman, Millet, & Chimes, 2011, p. 1143).
Compared to the evolution of the foot, the shoe is relatively new as it has only been around for a few thousand years. This places some doubt over their compatibility with the optimal biomechanical function of the foot (Wallden, 2010, p. 187). One of the main arguments used by supporters of conventional cushioned shoes is that humans did not evolve to run on hard concrete paths and bitumen roads (Downey, 2009). Considering that concrete and bitumen are as relatively new as shoes, evidence suggests that humans evolved in Africa, where for six months of the year, large areas of land are baked harder than concrete. There are major fossil finds that suggest our ancestors lived in the rocky environments of the Rift Valley, Olduvai Gorge or the volcanic regions of Laetoli (Wallden, 2010, p. 187). More importantly, there are still large populations of Africans who run barefoot on these rocky, baked surfaces. While many believe that the human foot requires cushioning as protection from the harsh conditions that we commonly run on today, there is sufficient evidence to suggest otherwise.
THE DEVELOPMENT OF THE RUNNING SHOE
In the late 1970s, the initial concept of the running shoe was developed because many concluded that the lower extremities of the foot are of poor biomechanical design with an unusually fragile structure that is ‘unable to sustain the use associated with running without injury, thus requiring additional protective devices’ (Rasch & Burke, 1978, p. 326). Since then the design of current running shoes, with ‘various heel cushioning strategies and technologies to increase medial support to control foot pronation’ (Novacheck, 1998), has become widely accepted as the industry standard. However there is no clinical evidence to support that modern shoe design promotes the long-term health of runners (Richards, Magin, & Callister, 2008). In fact, a decade of research shows that the rate of running related injury in distance runners has not declined despite the advances in footwear design and cushioning technologies (Novacheck, 1998) (Krabak, Hoffman, Millet, & Chimes, 2011, p. 1143). This is surprising considering that marketing claims otherwise.
The development of the shoe has led to an approach where it attempts to support a structure in the same way you support a broken bone in a cast (Wallden, 2010, p. 186); by treating it as a delicate object placed in a high impact environment and then wrapping it up in cushioning material to protect it (Robbins S. E., 1967, p. 149). This ultimately weakens the support musculature and bone structures within the foot with atrophy. Once these natural foot structures are weakened through the long-term use of footwear, the foot is left to rely on the external support structures provided by the footwear at fault. Unfortunately, the artificial support provided by the footwear does not compare to the natural support provided by the foot itself (Warburton, 2009, p. 3).
Recently, Nike were encouraged by their advisors to consider a ‘‘barefoot’’ alternative in order to keep the feet strong, and the athlete injury-free. The result of this advice was the birth of the ‘Nike Free’ (Wallden, 2010, p. 186). This proves that the forty year old idea of placing feet on thick polyurethane soles between the plantar aspect of the foot, and the ground might be seen to be undesirable. Current development of footwear encourages the mimicry of the natural foot function while ‘minimizing knee and hip joint torque’, reducing join torque to a level similar to that of barefoot running (Kerrigan, Franz, Keenan, Dicharry, Croce, & Wilder, 2009, p. 1062). The push by shoe manufactures towards minimalist and ‘barefoot’ alternatives in their footwear range acknowledges the benefits of running barefoot (Wallden, 2010, p. 188).
THE BIOMECHANICS OF SHOD RUNNING AND BAREFOOT RUNNING
Studies show that runners who run barefoot land on the front or middle of the foot first, before lowering the heel and transitioning body weight to the entire foot. The cushioned running shoe, allows runners to land comfortably on the heel before rolling weight forward on the foot. This movement and gait pattern is called shod running and shoe cushioning allows the distribution of the impact force, making a heel strike bearable (Sanders, 2010, p. 14).
Shod and barefoot – or unshod, are the two main gait styles associated with running and have different impacts on the body. A study conducted on 415 runners during a marathon illustrated that at the 15 km mark, 75% of runners exhibited a heel strike pattern (Hasegawa, Yamauchi, & Kraemer , 2007). Further studies have compared shod and unshod running that support the higher proportion of shod runners with a heel-strike pattern (Divert , Mornieux, Baur , Mayer, & Belli, 2005). The results from these studies and research from the Harvard Biomechanics lab show that the rear-foot strike pattern causes an abrupt and fast impact collision that leads to lower extremity forces of two times the body weight of the runner (Lieberman D. E., Venkadesan, Daoud, & Werbel, 2012). These findings add evidence to the reasoning that shoe companies add extra cushioning to the shoe in order to dissipate the lower extremity forces caused by a rear-foot strike pattern (Krabak, Hoffman, Millet, & Chimes, 2011, p. 1143). It is this impact that is considered to be the most basic element which causes running-related injuries.
In comparing the difference in lower extremity forces between running styles, a study was conducted in 2009 (Squadrone & Gallozzi, 2009) in which healthy male runners who were experienced in barefoot running and participated in a marathon barefoot, had the lower extremity forces analysed for barefoot, minimal footwear, and shod running. The study concluded with a decrease in the contact time and impact forces in the barefoot runner, while reporting greater plantar flexion at the ankle, a shorter stride length, higher stride frequency, and lower oxygen consumption in the barefoot and minimal shoe runner; rendering barefoot and minimal footwear running patterns more efficient (Krabak, Hoffman, Millet, & Chimes, 2011, p. 1144). Barefoot running compared with shod running produces substantially lower impact forces than those observed for rear-foot strike (Lieberman, Venkadesan, & Werbel, 2010) and resultant joint torque to the lower extremity, and greater conversion of energy to rotational energy, and is more efficient than shod running (Krabak, Hoffman, Millet, & Chimes, 2011, p. 1144).
IMPLICATIONS FOR INJURIES
Despite the development of the running shoe, practitioners of sports medicine have observed injuries in runners using every shoe model available (Robbins S. E., 1967, p. 149). Shoe design assumes that the musculature structure within the foot is beyond rehabilitation and therefore cannot, on its own, absorb impact through deflection on loading. The fact that injury rates have not decreased with the improvement of the running shoe is not an endorsement of the modern running shoe as a protective device, and indicates a failing in the basic assumptions used in running shoe design (Robbins S. E., 1967, p. 149). Injury rates in developing countries that have both shod and unshod population, such as Haiti, show a smaller lower extremity injury rate for the unshod or barefoot population. In Haiti specifically, barefoot weight bearing is ‘considered to induce resistance to lower extremity injury’ (Robbins S. E., 1967, p. 150).
The most frequently reported running injury is an ankle sprain, with ninety percent being ‘injuries causing partial or complete rupture of the anterior talobibular ligament’. (Robbins, Waked, & Rappel, 1995). An ankle sprain is generally caused by a decreased awareness of the position of the foot due to ‘a lack of feedback provided by the plantar cutaneous mechanoreceptors in direct contact with the ground’ (Robbins, Waked, & Rappel, 1995), or alternatively through the ‘twisting torque around the subtalar joint during a stumble’ (Stacoff, Steger, Stussi , & Reinschmidt, 1996).
One of the chronic injuries found in runners is plantar fasciitis, or the inflammation of the ligament that runs along the sole of the foot. Evidence suggests that the normally unyielding plantar fascia ‘acts as the support for the medial longitudinal arch, and that strain on the proximal fascial attachment during foot strike leads to plantar fasciitis’ (Robbins & Hanna, Running-related injury prevention through barefoot adaptations, 1987). Barefoot running, through proprioception may induce an adaptive running style that ‘transfers the impact to the yielding musculature, therefore reducing stress on the fascia’ and reducing plantar fasciitis incidents in barefoot runners’ (Robbins & Hanna, Running-related injury prevention through barefoot adaptations, 1987).
Various chronic ailments such as shin splints are attributed to ‘excessive pronation, supination, and shock loading of the lower limbs’ (Siff & Verkhoshansky, 1999, p. 451). During a barefoot run, the body compensates for a lack of cushioning underfoot by naturally plantar-flexing the foot at contact which enables a softer landing (Frederick, 1986). The natural flexing within the foot during barefoot running increases the total workload of the soft tissue support structures within the foot; increasing the overall strength of the musculature and soft-tissue structures and subsequently reducing the risk of injury (Yessis, 2000, p. 124).
The argument that the foot is incapable of rehabilitation of its natural intrinsic musculature structure and requires ‘arch support’ and similar assistance is unfounded. The foot is capable of rehabilitation of its naturally supporting structures through changes in the force-deflection characteristics of the main longitudinal arch of the foot with an increased weight-bearing activity while barefoot (Robbins S. E., 1967, p. 150). An experiment conducted over four months proved a positive change with a 5mm shortening of the medial longitudinal arch, and a subsequent lengthening of the arch when barefoot weight-bearing activities were suspended (Robbins S. E., 1967, p. 151). The shortening of the arch allows the foot to act as a dynamic impact dampening structure as it is naturally designed (Robbins S. E., 1967, p. 154). The shortening of the medial arch is verification that the foot is capable of rehabilitation and strengthening of its internal support structures (Robbins S. E., 1967, p. 152). In comparing shod and barefoot populations, there is confirmation that barefoot running populations have better arch development (Rao & Joseph, 1992) and that there is a lower occurrence of the most common running injuries (Warburton, 2009).
PROPRIOCEPTION AND THE EFFECT ON THE BRAIN
The foot is a part of a highly complex nervous system that provides sensory feedback to the brain; this is called the somatosensory system and it affects proprioception which is the brains awareness of the relative position of body parts and their movement. By providing the foot with a highly cushioned sole, it diminishes the perception of pain and pressure caused by impact on the highly sensitive plantar skin. This diminished sensory feedback does not induce the runner, through sensation, to diminish impact through using the ‘demonstrated medial arch adaptation nor to use other mechanisms, such as the alteration of his or her running mechanics to diminish impact’ (Robbins S. E., 1967, p. 152).
The modern running shoe and footwear in general have successfully diminished sensory feedback without diminishing the injury inducing impact. This type of injury follows the model of a neuropathic injury; a man-made device masks sensation and therefore does not allow protective behaviour (Robbins S. E., 1967, p. 151). Neuropathic injuries are caused by impaired somatosensory feedback. These injuries are a result of the illusion that the runner’s foot is well protected due to a lack of somatosensory feedback. Often the first sign of overload is an actual injury as the body, through proprioception, was not given the chance to provide protective adaption.
The adaptive behaviours caused by increased plantar tactile sensations include an improvement in overall balance during movement; simply because dynamic balance is dependant on ‘cutaneous and proprioceptive input from the foot’ (Bowser, McGrath, & Rose, 2010, p. 1). This is proven through research which highlights that balance is best in bare feet and instability increases between bare feet and Vibram Five Fingers, and between Vibram’s and conventional running shoes (Bowser, McGrath, & Rose, 2010, p. 2). This instability increase in balance is due to the filtering in sensory input caused by an increase in material between the ground and the foot. This improved balance s why gymnasts and dancers prefer to perform barefoot (Warburton, 2009, p. 2).
MINIMALIST SHOES AND VIBRAM FIVEFINGER
Understandably barefoot running is not always a practical option. Ground surfaces are often unsuited for barefoot running because of the risk of injury from stones, glass, and other debris. These risks are mitigated by the use of ‘minimalist’ or ‘functional’ footwear, which is footwear designed to mimic barefoot running while still providing sufficient protection to the sole of the foot. In recent years, Nike, Masai Barefoot Technology, FitFlop, VIVO, Newton and Vibram have all released minimalist footwear.
There is criticism from sports medicine physicians that minimalist footwear, specifically Vibram FiveFingers, has little research to substantiate their use; as the current research available suggests ’a dramatic change of the gait pattern, and the way the user runs, they could be dangerous and might well cause as many injuries as might be prevented’ (Squadrone & Gallozzi, 2009). This is interpreted either as a dramatic change to what the runner is used to; or a dramatic reversion to what the individual is designed for.
Nike Free. Developed in 2004 in response to barefoot running observations made by Nike representatives, the Nike Free is designed to provide less cushioning and restriction than the conventional shoe. The Nike Free comes in several models, ranging from V3 to V7, where the increase in version number correlates to the amount of cushioning and restriction provided by the shoe. Typically, the Nike Free V7 has a similar amount of cushioning to that of a conventional running shoe. In developing the Nike Free running shoe, they gathered information regarding barefoot function while running on grass, they created a shoe to allow close mimicry of the barefoot kinematics observed. Nike then partnered with Prof. Peter Brueggemann at the University of Koln to conduct a study with 100 athletes participated over a period of four months; to which Nike concluded the study with the result that the Nike Free improved flexibility, strength and balance leading to better performance and lower injury risk (Wallden, 2010, p. 187).
VIVO Barefoot. Developed by VIVO, the ‘Barefoot’ is a minimalistic shoe with an ultra-thin, 3mm puncture resistant sole. The marketing literature for VIVO details that with 200,000 nerve endings, the lack of cushioning strengthens the foot naturally by ‘encouraging the muscles of the feet to work, stimulating every nerve ending to enhance sensory perception’ (Wallden, 2010, p. 187).
Vibram FiveFinger. Vibram is a world leading sole manufacture specialising in rugged, hard-wearing, gripping soles for industrial and mountaineering boots. Initially the FiveFinger shoe was designed to give sailors the sensation of being barefoot while providing a protective and gripping sole; allowing a more natural feeling to sailing. The functionality and use of FiveFingers quickly expanded beyond sailing to the running community as they provided the required protection needed by the foot while still maintaining a pure barefoot running style.
The first research into FiveFingers was conducted in March 2009, which detailed the biomechanical effect of wearing FiveFingers footwear. It compared shod running, barefoot running and ‘Fivefingered running’ and concluded that running in Vibram FiveFingers ‘creates an almost identical posturing of ankle, knee and hip compared to the natural barefoot state’ (Squadrone & Gallozzi, 2009). Similarly to running barefoot, running in Vibram FiveFingers results in a midfoot or forefoot strike, compared to the heel strike of shod running. This running style increases the stiffness requirement of the lower limb which is required for effective load transfer.
There is also substantial fear, uncertainty and doubt surrounding the use of Vibram FiveFingers due to their accelerated uptake as running shoes. This doubt and uncertainty is caused by a number of stress related injuries to users new to ‘barefoot’ running. When switching from a heal-strike shod running gait, to a midfoot or forefoot style, there is a significant difference in the muscle groups being utilised in motion, and an increased loading on the 2nd metatarsal head within the foot (Wallden, 2010, p. 191). These injuries are caused by a lack of transition training to strengthen the foot and muscle groups that are now being utilised. An instructional card is supplied when purchasing Vibram FiveFingers that provides an eight week transition training plan that begins at walking, to light jogging on grass, to distance running on hard surfaces, specifically to avoid injury.
A unique difference that separates Vibram FiveFingers from other minimalist shoe designs is the separate toe compartments. This is designed specifically to allow the natural separation of the toes so they can act more proprioceptively, across their entire range of motion and lateral spread; improving frontal plane stability (Wallden, 2010, p. 192). The natural separation of the toes allows for the foot to function as it was originally designed.
The human foot has been in development for millions of years, in the relative time span of events, the cushioned running shoe is a very new development. With forty years of cushioning and design enhancements there is no evidence to support the popular belief that running shoes reduce injury; there is concern however that the long-term effects of running shoes actually increase the rate of injury due to atrophy in the internal support structures of the foot and the reduction in sensory feedback.
There is a significant difference in the impact loading of the lower extremities between a shod and unshod runner; where a heel strike causes a spike in impact. Conventional running shoes are designed to cushion the heel to allow a heel-strike style rather than adapting the running style to reduce impact – through a forefoot or mid-foot strike. Minimal footwear has been designed to allow a natural mid/forefoot running style through a reduction of cushioning to increase sensory feedback; allowing the brain to adjust its body movement and running gait in order to become more efficient.
While running barefoot is not ideal in many scenarios due to glass, sharp objects and other man-made environmental hazards; the risks these hazards pose are mitigated through the use of minimalist footwear that is designed to provide a near-barefoot environment while protecting the foot from puncture with durable soles.