Locomotor effects of shoes are the way in which the physical characteristics or components of

shoes A shoe is an item of footwear intended to protect and comfort the human foot. They are often worn with a sock. Shoes are also used as an item of decoration and fashion. The design of shoes has varied enormously through time and from culture t ...

influence the locomotion neuromechanics of a person. Depending on the characteristics of the shoes, the effects are various, ranging from alteration in balance and posture, muscle activity of different muscles as measured by electromyography ( EMG), and the impact force. There are many different types of shoes that exist, such as running, walking, loafers, high heels, sandals, slippers, work boots, dress shoes, and many more. However, a typical shoe will be composed of an insole, midsole, outsole, and heels, if any. In an unshod condition, where one is without any shoes, the locomotor effects are primarily observed in the heel strike patterns and resulting impact forces generated on the ground.

Insoles and inserts

The foot provides the sensory information to the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all pa ...

through cutaneous afferent feedback, which originates from the special

mechanoreceptors A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, ...

within the plantar surface of the foot. This afferent feedback has a strong influence on postural stability and balance correction during standing and walking. Since sensory feedback from the foot may be influenced by the interaction of the foot with the insole surface, different types of insoles and shoe inserts have been used to try to enhance postural stability.

Textured inserts

Textured Inserts are regular shoe inserts that have a raised textured surface on the side that acts to provide enhanced mechanical contact and pressure on the plantar surface of the feet. Providing a textured surface of the shoe insert leads to significant changes during gait in ankle joint

kinematics Kinematics is a subfield of physics, developed in classical mechanics, that describes the motion of points, bodies (objects), and systems of bodies (groups of objects) without considering the forces that cause them to move. Kinematics, as a fi ...

and in EMG amplitude of ankle flexor and extensor muscles. Textured inserts mostly affect ankle motion in the

sagittal The sagittal plane (; also known as the longitudinal plane) is an anatomical plane that divides the body into right and left sections. It is perpendicular to the transverse and coronal planes. The plane may be in the center of the body and divid ...

plane, where plantar flexion of the foot is increased. As for muscle activity, textured inserts decrease the activation of

soleus In humans and some other mammals, the soleus is a powerful muscle in the back part of the lower leg (the calf). It runs from just below the knee to the heel, and is involved in standing and walking. It is closely connected to the gastrocnemius ...

and

tibialis anterior The tibialis anterior muscle is a muscle in humans that originates along the upper two-thirds of the lateral (outside) surface of the tibia and inserts into the medial cuneiform and first metatarsal bones of the foot. It acts to dorsiflex and inve ...

muscles during standing and walking.

Insoles with ridges

One of the most pervasive effects of aging is the loss of

cutaneous Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different de ...

and pressure sensation, which has been correlated with impaired balance control and increased risk of

falling Falling or fallin' may refer to: *Falling (physics), movement due to gravity *Falling (accident) * Falling (execution) * Falling (sensation) People * Christine Falling (born 1963), American serial killer who murdered six children Books * ''Fa ...

. This is because for an upright stance, the

center of mass In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force may ...

(COM) of the body must be positioned over the base of support (BOS) established by the feet. Cutaneous feedback from the feet is necessary to provide the

(CNS) with the information about the proximity of the COM to the BOS limit, which is an important parameter for the maintenance of balance and stable gait.Menant, JC., Perry, SD., Steele, JR., Menz, HB., Munro, BJ. Effects of Shoes Characteristics on Dynamic Stability When Walking on Even and Uneven Surfaces in Young and Older People. Archives of Physical Medicine and Rehabilitation. 89(10):1970-6. 2008 Oct. Since plantar pressure sensation aids in balancing reactions in stepping movements, insoles with raised ridges along the edges can enhance stimulation of cutaneous mechanoreceptors that help to define the BOS. Most of the time, the ridges are made so that stimulation only occurs when the COM nears the BOS limit. Insoles with ridges appear to reduce the likelihood that the COM motion will exceed the BOS limit in the lateral direction, thereby resulting in a stabilizing effect on gait. Furthermore, the magnitude of this effect did not diminish with time, which suggests the CNS did not habituate to heightened cutaneous stimulation. Therefore, insoles with ridges can aid in reducing the fall rates among elderly populations.

Midsole

The

midsole A shoe is an item of footwear intended to protect and comfort the human foot. They are often worn with a sock. Shoes are also used as an item of decoration and fashion. The design of shoes has varied enormously through time and from culture to ...

is between the outer sole (bottommost) and the insole (topmost) parts of the shoe sole. It can be made of a variety of materials to give the shoe different mechanical characteristics of cushioning, support, and flexibility.

Polyurethane Polyurethane (; often abbreviated PUR and PU) refers to a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane is produced fro ...

midsoles are denser and more supportive while

ethylene vinyl acetate Ethylene-vinyl acetate (EVA), also known as poly (ethylene-vinyl acetate) (PEVA), is the copolymer of ethylene and vinyl acetate. The weight percent of vinyl acetate usually varies from 10 to 40%, with the remainder being ethylene. There are thr ...

is used to make lighter and more compliant midsoles.

Density/stiffness

By changing the material hardness of the midsole, one will be able to change the EMG activity in various lower extremity muscles such as

rectus femoris The rectus femoris muscle is one of the four quadriceps muscles of the human body. The others are the vastus medialis, the vastus intermedius (deep to the rectus femoris), and the vastus lateralis. All four parts of the quadriceps muscle attach to ...

biceps femoris The biceps femoris () is a muscle of the thigh located to the posterior, or back. As its name implies, it has two parts, one of which (the long head) forms part of the hamstrings muscle group. Structure It has two heads of origin: *the ''long h ...

, medial

gastrocnemius The gastrocnemius muscle (plural ''gastrocnemii'') is a superficial two-headed muscle that is in the back part of the lower leg of humans. It runs from its two heads just above the knee to the heel, a three joint muscle (knee, ankle and subtalar ...

, and

. Especially when running with the stiffer midsole, the EMG amplitude for

have shown to be significantly greater before the heel strike and lower following the heel strike than compared to the neutral midsole. Furthermore, walking in shoes with stiffer midsole appears to significantly reduce the energy dissipated at the metatarsophalangeal joints and aid in improving jumping performances and

running economy Running economy (RE) measures runners' energy utilization when running at an aerobic intensity, and many physiological and biomechanical factors contribute to it. Oxygen consumption (VO2) is the most commonly used method for measuring running e ...

. However, the underlying mechanisms that can be attributed to this improvement are still not fully understood.

Midsole wedging

With the increasing number of injuries associated with excessive

pronation of the foot Pronation is a natural movement of the foot that occurs during foot landing while running or walking. Composed of three cardinal plane components: subtalar eversion, ankle dorsiflexion, and forefoot abduction, these three distinct motions of t ...

, much research has been conducted with different types of midsoles that could possibly aid in prevention of such injuries. The varus-wedged shoes, which have a medial incline, seem to decrease

pronation Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

during stance time, reduce the net inversion of the joint moment, and decrease the activities of the inverter muscles, such as

tibialis posterior The tibialis posterior muscle is the most central of all the leg muscles, and is located in the deep posterior compartment of the leg. It is the key stabilizing muscle of the lower leg. Structure The tibialis posterior muscle originates on the ...

, and

. The valgus-wedged shoes, which have a lateral incline, are designed to accentuate pronation and have the opposite effect as the varus-wedged shoes. Also when walking in valgus-wedged shoes, it may lead to an increase in calcaneus eversion and up to 58% of energy absorption in the frontal plane of the body.

Heel curvature

Rocker bottom shoes have thicker-than-normal soles with rounded heels, and most varieties of the shoes are constructed such as to shift the wearer's body weight to behind the ankle, therefore finding the balance requires more effort.

Heel height

Shoe heel height can have significant biomechanical effects on the shoe wearer that can be detrimental or beneficial.

High heels

High heels High-heeled shoes, also known as high heels, are a type of shoe with an angled sole. The heel in such shoes is raised above the ball of the foot. High heels cause the legs to appear longer, make the wearer appear taller, and accentuate the ...

are shoes where the rearfoot (the heel) is positioned higher than the forefoot (toes). High heels of various heights are worn by men and women on a daily basis. The main reason many people wear high heeled shoes is for aesthetic purposes, where high heels are believed to enhance the wearer's physical appearance. These same high heeled shoes, however, can have undesirable biomechanical effects. During gait, high heeled shoes are shown to affect the ankle joint, causing significantly increased

plantarflexion Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

. This, in turn, increases the metabolic costs of walking and leads to faster muscle fatigue. Accelerated muscle fatigue may then increase the likelihood of ankle sprains and or falls due to impaired foot and ankle stability. Wearing high heels can also lead to shorter stride lengths, greater stance time, unstable posture and gait, and a decrease in lumbar flexion angles. Changes to muscle activity are also observed with high heeled shoes, mostly affecting the

and

erector spinae The erector spinae ( ) or spinal erectors is a set of muscles that straighten and rotate the back. The spinal erectors work together with the glutes ( gluteus maximus, gluteus medius and gluteus minimus) to maintain stable posture standing or sitt ...

muscles. The increase in plantar flexion of the foot causes the EMG amplitude of tibialis anterior to increase. The high heels also lead to an increase in the lumbar flexion angle due to a compensatory mechanism to prevent one from falling forward. In addition, increased heel height may lead to numerous foot problems including: *

callus A callus is an area of thickened and sometimes hardened skin that forms as a response to repeated friction, pressure, or other irritation. Since repeated contact is required, calluses are most often found on the feet and hands, but they may o ...

es *foot pain *

blister A blister is a small pocket of body fluid (lymph, serum, plasma, blood, or pus) within the upper layers of the skin, usually caused by forceful rubbing (friction), burning, freezing, chemical exposure or infection. Most blisters are filled w ...

s *

hammer toe A hammer toe or contracted toe is a deformity of the muscles and ligaments of the proximal interphalangeal joint of the second, third, fourth, or fifth toe causing it to be bent, resembling a hammer. In the early stage a flexible hammertoe is ...

s *

bunion A bunion, also known as hallux valgus, is a deformity of the joint connecting the big toe to the foot. The big toe often bends towards the other toes and the joint becomes red and painful. The onset of bunions is typically gradual. Complicatio ...

s (hallux valgus) *

Morton's neuroma Morton's neuroma is a benign neuroma of an intermetatarsal plantar nerve, most commonly of the second and third intermetatarsal spaces (between the second/third and third/fourth metatarsal heads; the first is of the big toe), which results in t ...

metatarsalgia Metatarsalgia, literally metatarsal pain and colloquially known as a stone bruise, is any painful foot condition affecting the metatarsal region of the foot. This is a common problem that can affect the joints and bones of the metatarsals. Meta ...

*ankle sprain *shortened Achilles tendons *high heel cords *

osteoarthritis Osteoarthritis (OA) is a type of degenerative joint disease that results from breakdown of joint cartilage and underlying bone which affects 1 in 7 adults in the United States. It is believed to be the fourth leading cause of disability in the ...

in the knee. In contrast, moderate heel elevation has also been used as a conservative treatment for

plantar fasciitis Plantar fasciitis or plantar heel pain (PHP) is a disorder of the plantar fascia, which is the connective tissue which supports the arch of the foot. It results in pain in the heel and bottom of the foot that is usually most severe with the fi ...

to decrease strain in the

plantar fascia The plantar fascia is the thick connective tissue (aponeurosis) which supports the arch on the bottom ( plantar side) of the foot. It runs from the tuberosity of the calcaneus (heel bone) forward to the heads of the metatarsal bones (the bone bet ...

. Although various locomotor effects of heels are prominent, the practical health implications are still debatable.

Negative heels

Negative heeled shoes, which are also known as earth shoes, are shoes that are designed to mimic uphill walking to increase the resistance training effect on the leg muscles during normal walking. The forefoot(toes) of the shoe is 1.5 cm higher than the heel of the shoes, creating an approximately 10 degree angle of dorsiflexion at the ankle during stance on level ground. Walking in negative heeled shoes leads to a faster

cadence In Western musical theory, a cadence (Latin ''cadentia'', "a falling") is the end of a phrase in which the melody or harmony creates a sense of full or partial resolution, especially in music of the 16th century onwards. Don Michael Randel (1 ...

and shorter stride length, resulting in a significantly shorter stride cycle time than when walking with a natural cadence. The range of the ankle motion is also significantly greater in the negative heeled shoes, remaining in dorsiflexion longer throughout the stance and swing phases of gait. The increased duration of dorsiflexion leads to lengthening of the gastrocnemius and soleus muscle-tendon units and the length of the moment arm of the Achilles tendon. A similar post-operative exercise effect involving increased dorsiflexion is often desired after surgeries involving the gastrocnemius and soleus muscles or

Achilles tendon The Achilles tendon or heel cord, also known as the calcaneal tendon, is a tendon at the back of the lower leg, and is the thickest in the human body. It serves to attach the plantaris, gastrocnemius (calf) and soleus muscles to the calcane ...

. The purpose of the exercise is to increase the range of motion in the ankle joint and strengthen the gastrocnemius and soleus muscles and the Achilles tendons. Wearing negative heeled shoes, therefore, may offer an alternative method for post-operative rehabilitation in these situations. Although dorsiflexion of the ankle may be beneficial, it also causes the center of gravity to shift backward, which can cause instability and difficulty in propelling forward during gait. When walking in negative heeled shoes, muscle activity of gastrocnemius and tibialis anterior muscles are similar to that observed in uphill walking. The duration of the EMG activity is longer and the EMG amplitude is higher for the calf and the

muscles than compared to normal shoes. Also the EMG readings for the

and

indicate an enhanced co-contraction of the two muscles, and therefore the negative heeled shoes may be helpful in exercising these muscle groups.

Barefoot (unshod)

Unshod condition is where one is without any shoes, or is

barefoot Barefoot is the state of not wearing any footwear. There are health benefits and some risks associated with going barefoot. Shoes, while they offer protection, can limit the flexibility, strength, and mobility of the foot and can lead to h ...

. Much of the research on unshod locomotion has been conducted on

barefoot running Barefoot running, also called "natural running", is the act of running without footwear. With the advent of modern footwear, running barefoot has become less common in most parts of the world but is still practiced in parts of Africa and Latin Am ...

. However, some of the learned principles may apply to both running and walking.

Foot strike patterns

Barefoot runners run very differently from typical shod runners. Shod runners tend to heel strike due to the designs of the modern shoes, which have thick heels to reduce the impact force from the ground. When running barefoot, however, some runners tend to shift to a forefoot striking pattern to avoid such impact, which is equivalent to 2-3 times the body weight.Lieberman, DE, Venkadesan, M, Werbel, WA, Daoud, AI., D’Andrea, S. Davis, IS. Foot Strike Patterns and Collision Forces in Habitually Barefoot versus Shod Runners. Nature 463:531-535. 28 January 2010. The forefoot strike is where the forefoot lands first, followed by the heels coming down. The midfoot strike is characterized by the heel and the ball of the foot landing at the same time, and heel strike is where the heel lands first followed by the forefoot.

Impact forces

In barefoot locomotion, the impact force (impact transient) on the ground is diminished compared to shod running. It has been suggested that unshod runners are better able to take advantage of elastic energy storage in the Achilles tendon and arch of the foot, and can avoid potential injury due to repetitive impact of the heel bone (

calcaneus In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock. St ...

) due to heel striking. However, the long-term and actual health benefits of unshod running are still not well understood and remain an area of active research. Those who wish to approximate the experience of running barefoot, but would prefer some protection, can resort to shoes that mimic barefoot locomotion. Such shoes as water socks, running

sandals Sandals are an open type of footwear, consisting of a sole held to the wearer's foot by straps going over the instep and around the ankle. Sandals can also have a heel. While the distinction between sandals and other types of footwear can some ...

moccasins A moccasin is a shoe, made of deerskin or other soft leather, consisting of a sole (made with leather that has not been "worked") and sides made of one piece of leather, stitched together at the top, and sometimes with a vamp (additional panel o ...

, huaraches, dime-store plimsolls, Vibram FiveFingers footwear and other minimal running shoes have relatively thin soles but provide some protection. However minimal shoes do not give runners the same feedback from the plantar

mechanoreceptor A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, ...

s. Because of the greater protection they offer in comparison to barefoot running, minimal shoes may also interfere with the development of a gentle foot strike, toughening of the soles of the feet, and awareness of road hazards.

References

{{Reflist

External links

Dr.Lieberman's Lab Website for the Barefoot Runners
Biomechanics Shoes