By Emily Splichal, DPM, MS, CPT
Running is one of the most common forms of exercise and has benefits ranging from weight loss to cardiovascular conditioning. Despite the millions of dollars spent on research to advance shoe design and orthotic modifications, there is still a high rate of lower extremity injuries in runners. A 2007 review by Wen estimates that injury rates vary from 37% to 79%, depending on the type of population studied.1 Wen found the most common injuries among runners were chronic or overuse in nature, and patellofemoral pain syndrome, Achilles tendinopathy, and shin splints were the most common.1 As a result of the high injury rate there has been a revived trend of runners kicking off their sneakers and opting to run barefoot in the hopes of reducing injury risk.
Does this mean the benefits of barefoot running are worth saying goodbye forever to the running shoe? Not necessarily. Conflicting data2 regarding the risks and benefits of barefoot running warrant a look at different techniques for reducing overuse injuries in runners.
However, barefoot training is one of two training techniques that have shown promise for reducing knee and foot injuries in runners, which are the most common lower extremity running injuries.1 Another promising technique for reducing these injuries is balance training. Although no studies to date have evaluated the combined benefits of these two training techniques, the positive results associated with each technique suggest that balance training combined with barefoot training could lead to a further reduction in lower extremity injury risk.
A 2005 study by Geraci et al3 supports strength training exercises for runners that integrate foot and hip function, such as balance reaches, single leg squats, and step downs. These activities are beneficial as they activate the entire functional kinetic chain, from the rearfoot position to the gluteus medius.3 Other benefits include those found by Robbins et al,4 who reported positive changes in arch height and rearfoot position with prolonged barefoot exercises. They also noted enhanced proprioceptive and sensory feedback as barefoot adaptations that could reduce injuries among runners.4
Three key potential benefits of barefoot balance training for reducing running-related injuries include improved attenuation of ground reaction forces, improved rearfoot position, and increased hip strength. Barefoot training addresses the first two variables, while balance training addresses the third.
Ground reaction force and injury risk
Every step translates a ground reaction force (GRF) through the body averaging one to 1.5 times body weight.5 Increase pace to a running cadence and GRF increases to up to three times body weight.5
As the interface between the ground and the rest of the body, the foot plays an important role in absorption and dissipation of GRF. Increased foot mobility and decreased intrinsic foot strength have been associated with overuse injuries related to poor attenuation of GRF.6
Shoe companies have responded to injury risk associated with GRF by integrating shock-absorbing technology into running shoes. Yet runners still experience overuse injuries related to poor absorption of GRF. This is where we must look at barefoot or minimalist running mechanics. Studies demonstrate low rates of some lower extremity injuries in barefoot runners, which is hypothesized to be the result of decreased GRF and the more effective dissipation of forces that occurs in the barefoot condition.7 It may be possible to take some of these principles and apply them to the shod rearfoot striker.
Like the human hand, the plantar aspect of the human foot is highly sensitive, with a dense network of mechanoreceptors and nociceptors that respond to both the amount and rate of pressure experienced. When the foot senses the vertical GRF associated with each step, its design allows it to dissipate those forces through an innate loading response.6
Beginning with heel strike, GRF is attenuated initially through contraction and deceleration of the posterior tibialis muscle. As the foot continues through midstance, the intrinsic foot musculature contracts and the hip begins to flex to absorb the remaining GRF.
The accuracy of this innate loading response is correlated with the foot’s perception of GRF. Studies have suggested that footwear impairs this perception, resulting in an inadequate loading response and increased stress on the body.7,8
To further assess the role of plantar cutaneous receptors on perception of plantar load, a study by Robbins et al8 compared responses from three foot conditions: shod, barefoot on a flat surface, and barefoot on a gravel surface. Robbins et al demonstrated that, compared with barefoot conditions, shod participants consistently underestimated the magnitude of an applied plantar load. Between the two barefoot conditions, the most accurate perception of load response was in individuals who were barefoot on gravel.8
This study not only illustrates the role of plantar receptors in accurate foot load perception but also suggests running shoe design may play a role in the incidence of running related injuries. A 2009 review by Richards et al9 concluded that the typical running shoe today features pronation control and an elevated cushion heel. Interestingly, since the introduction of this shoe design there has been an increase in running related injury to the Achilles tendon.8,10
A vital component of the innate loading response is contracture of the intrinsic foot musculature. The stronger the intrinsic muscles, the more effective they will be at dissipating ground reaction forces. It has been suggested that shoes weaken the intrinsic foot muscles, which are not required for quiet stance in shod conditions.6
Robbins et al also demonstrated no tonic electromyographic activity in the intrinsic foot musculature during shod quiet stance. Interestingly, this same study demonstrated an increase in intrinsic tonic activity after several months of barefoot training, as well as an increase in medial arch height. This study suggests that barefoot training may improve intrinsic muscle strength and thereby improve dissipation of GRF.8
Rearfoot position and injury risk
The second factor associated with an increased risk of running-related injuries is rearfoot position. Rearfoot position may have an influence on lower extremity injury rates through mechanical joint coupling between the subtalar joint and the knee.11
This coupled motion between the talus and tibia has been supported by numerous studies, including a study by Williams et al12 that demonstrated the impact of increased calcaneal eversion as it relates to knee injury risk. Williams et al found that low-arched runners with increased calcaneal eversion had greater incidence of medial knee injuries and tendinopathies compared with high-arched runners.12 Conversely, in a high-arched foot that exhibits increased calcaneal inversion at heel strike, injuries tended to be more related to impaired shock absorption and lateral ankle injuries.12
Stabilization of the rearfoot at heel strike is multifactorial and includes the dynamic stabilization of supporting foot musculature as well as proximal activation of hip external rotators.13 A study by Snyder et al evaluated the effect of six weeks of gluteus medius and hip external rotator strengthening on rearfoot kinematics during running. In the study, 15 women with moderate pronation (average calcaneal eversion, 5º) and normal arch height participated in single leg stance, hip external rotator exercises three days a week. After six weeks, women demonstrated significant increases in hip external rotator strength and decreased knee abduction moment, rearfoot inversion moment, rearfoot eversion range of motion, and rearfoot eversion velocity at heel strike.13
Although the women did not have an excessively overpronated foot type, this study supports the effectiveness of proximal hip strengthening on distal foot function. This associated improvement in foot function and rearfoot motion should decrease valgus stress on the knee and hopefully reduce the incidence of knee injuries in runners.
A study by Feltner et al14 evaluated the impact of foot-specific strengthening programs on rearfoot position at heel strike and the efficacy of such an application in reducing knee injury risk among runners. Feltner et al compared the impact of a foot invertor and evertor muscle-specific strengthening program with traditional ankle rehabilitation exercises on rearfoot position at heel strike and degree of midfoot pronation. After an eight-week strengthening program, Feltner and colleagues observed decreases in rearfoot eversion (reduced by 2.2º) and midfoot pronation (2.9º) in only the invertor-specific strengthening program.14
Hip strength and injury risk
Barefoot balance training may also decrease knee injury risk. Because the knee is positioned between the foot and ankle distally and the hip proximally, an imbalance in either joint will negatively affect the knee. Among runners, the most common knee injury is patellofemoral pain syndrome.
Patellofemoral pain syndrome is anterior/lateral knee pain with activity, descending stairs, or prolonged sitting. Reports suggest that patellofemoral pain syndrome is a very common, if not the most common, disorder in a sports medicine or rehabilitation institution.3 Many factors can contribute to patellofemoral pain syndrome, but lateral patellar maltracking is the most common symptom.3
Research suggests abnormal subtalar joint motion in particular may lead to patellofemoral malalignment.15 Excessive rearfoot eversion may lead to abnormal knee internal rotation, which may translate to greater stresses on knee structures and alter patellar tracking. Although studies to date have been inconclusive as to whether rearfoot position or rearfoot motion has greater impact on knee injury rates, both variables require hip strength to counter internal tibial rotation forces.16
Diminished hip strength has been implicated as a contributor to abnormal knee alignment and patellofemoral pain. A 2003 study by Ireland et al17 evaluated whether young women with patellofemoral pain were more likely to demonstrate weakness in hip abduction as well as external rotation than age-matched women who were not symptomatic. Ireland and colleagues found that the women with patellofemoral pain demonstrated 26% less hip abduction strength and 36% less hip external rotation strength compared with the controls.17
As a podiatrist and human movement specialist, I believe all patients should undergo a thorough biomechanical and functional assessment. Functional movement tests such as squats, single leg balance, and step ups offer insight into the function of the foot and ankle during daily activities or sport. Functional testing will reveal any muscle imbalances and compensations proximally that may be influencing foot posture and rearfoot position.
Although no studies to date have evaluated the combined benefits of barefoot training with balance training, this is a technique I have used in many patients and athletes presenting with classic overpronation and lower crossed syndrome (low back and lower extremity pain related to postural imbalance). The benefits I have observed in my patients lend support to the possible application of this training technique.
An example of potential benefits can be illustrated with a case study of one of my patients. A man, aged 31 years, presented with bilateral pes planovalgus and complaints of bilateral medial knee pain, which were greater in the left knee than the right. The patient was unable to run long distances due to his knee pain. On physical exam, I noted the patient had bilateral decreased ankle dorsiflexion, a bilateral increase in calcaneal eversion, decreased medial arch height during relaxed stance, and a bilateral increase in knee adduction during single leg step up and single leg squat.
The patient was not interested in orthotic intervention; therefore I recommended a program of posterior group stretching and posterior tibialis activation exercises followed by 20 minutes of barefoot balance exercises targeting the gluteus medius and hip external rotators. The barefoot balance training program was performed three times a week for six weeks. At six-week follow up, the patient reported decreased knee pain and foot fatigue. On physical exam, he demonstrated decreased knee adduction during single leg squat and decreased calcaneal eversion during stance compared with the initial exam.
From the stimulation of plantar cutaneous receptors to the strengthening of intrinsic foot musculature and hip external rotators, barefoot balance training addresses the functional kinetic chain imbalances that commonly contribute to lower extremity injuries in runners. By understanding the integrated function of the foot and hip on the lower extremity, practitioners can more effectively recommend strength training techniques such as barefoot balance training, which specifically addresses factors that put runners at risk for overuse injuries.
Emily Splichal, DPM, MS, CPT, is a human movement specialist and founder of the Evidence-Based Fitness Academy in New York, NY.
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