Understanding the foot and how it functions is important in understanding the structure and function necessary for the body to withstand a lifetime of activity. After all, the muscular support that creates the body’s passive architecture—which allows, for example, the fundamental function
of gait—begins at the foot.

Gait is a complex activity. The ground first touches the foot near the lateral aspect of the heel and then passes under the middle of the foot. It then makes contact just below the third toe and finally touches the great toe as the body propels through push-off, creating a unique pattern of pressure on the sole. Assessing gait cycle and understanding ideal gait patterning take practice and a keen eye, but being able to identify misalignment or poor gait can be a platform for designing strategic and successful training programs. Although often overlooked, the foot is a vital part of this system that cannot be compromised.

Why the Foot Is So Important

The foot itself is an architectural structure often called the “plantar vault,” which unites all of the foot’s joints, ligaments and muscles into an adaptable system. The structural arrangement of these elements creates the arches, curvature and elasticity crucial in distributing the weight of the body, giving the foot its flexibility and shock absorption and adapting the shape of the plantar side of the foot to the surfaces that it encounters during gait. The plantar vault can adapt to ground forces in relation to body weight and uneven terrain to achieve the best mechanical advantage under the most varied conditions. However, flattening or exaggeration of the curvature of the foot can seriously compromise the support necessary for running, walking and maintaining proper body alignment.

Wide at the front just below the toe line and tapering near the heel, the foot is a sort of tripod upon which the body balances. The three points of this tripod are the posteroinferior tuberosity of the calcaneus, the head of the first metatarsal and the head of the fifth metatarsal, and three arches connect them. The anterior arch runs from the head of the first metatarsal to the head of the fifth metatarsal. The medial arch, the highest and most noticeable of the arches, runs from the head of the first metatarsal to the posteroinferior tuberosity of the calcaneus and is mostly involved in the propulsion phase of gait. The lateral arch runs from the head of the fifth metatarsal to the posteroinferior tuberosity of the calcaneus and is occupied by muscle, so it is not visually obvious. (The lateral edge of the foot contacts the ground and is more involved in supporting weight-bearing mechanics during walking or running.)

The transverse curvature of the foot, which involves the entire length of the foot, is supported by muscles such as the adductor hallucis, peroneus longus and tibialis posterior. The longitudinal curvature of the foot depends on the strength and synergy of the abductor hallucis, flexor hallucis longus and abductor digiti minimi. Indeed, many of the muscles discussed in this article as movers also have the important role of stabilizing the arches and curvatures of the foot necessary for ideal body alignment.

Ideally, when one stands, the weight of the leg is distributed equally forward and backward from the ankles. Half of the body’s weight rests on the balls of the feet; the other half rests on the heels. The center of the knee should be in line with the base of the third toe.

In discussing movements of the foot, one can refer either to movement of
the entire foot—such as dorsiflexion or plantar flexion, described in the previous article on the ankle and lower leg (IDEA Personal Trainer, February 2003, pp. 52-56)—or to movement within a specific region of the foot or movement of a joint within the foot structure. For example, the push-off at the great toe, which operates independently from the other toes, affects gait efficiency. As you examine the muscles of the foot, you will see how they provide support, strength and integrity for maintaining body stability.

A Kinesiological Look
at the Foot

The joints in each foot provide two functions:

Support. Whereas the ankle controls foot movements in the sagittal plane, the joints within the foot allow the sole to interface with the ground correctly and efficiently with respect to the other two planes.

Locomotion. The feet carry the body through space and, thanks to human reflexes, can adapt to changes in terrain quickly; one must understand this instantaneous transformation from weight-bearing mechanism to lever to understand compensatory patterns in the body. Mobility at the base of the supporting limb is critical for locomotion. In gait, a moment of apparent “falling forward” must occur with freedom while the pivotal system created by the foot and ankle preserves gait momentum and control. The heel, ankle and forefoot serve as rockers that allow the body to advance while the knee maintains a basically extended posture. Forward progress occurs because the ankle muscles yield yet restrain the ankle joint in a fluid yet mechanical fashion.

The timing of muscle action in the ankle is very phasic; the plantar flexors are consistently active in stance. The neurological timing of muscle contractions in the lower leg and foot significantly influences the phasic clarity of the ankle muscles and functional potential of gait. The actual motion of gait is the result of synergy among all of the body’s parts. Everything from the ability of the abductors to stabilize the pelvis as the body’s weight shifts from one leg to the other, to the forward swing of the opposite limb, provides the proper force to propel the body.

In the foot are four layers of muscles, all of which facilitate movement of the toes and, along with the ligaments, support the structure of all of the joints within the foot. Most of the muscles on the dorsal side of the foot are actually the distal ends of the muscles of the lower leg and were discussed in the previous article; the extensor digitorum brevis and interossei are the only dorsal intrinsic muscles used in movement of the toes. The other three layers of foot muscles are plantar layers.

THE DORSAL LAYER

The extensor digitorum brevis originates from the anterosuperolateral calcaneus and divides into four tendons: The medial tendon inserts on
the proximal phalanx of the great toe, and the other three merge laterally with the tendons of the extensor digitorum longus (discussed in the previous article) and insert on the second, third and fourth toes. Together with the extensor digitorum longus, the extensor digitorum brevis aids dorsiflexion of the first four toes.

The fourth and most intrinsic layer of foot muscles consists of two layers
of interossei, fibrous muscles that lie between the toes and expand them. The three plantar interossei allow adduction of the third, fourth and fifth toes. The four dorsal interossei allow abduction of the second, third and fourth toes; they originate in a wide, fibrous manner between the toes and insert on the proximal phalanges at the base (plantar side) and tendon (dorsal side) of the extensor digitorum longus. Together, these muscles work predominantly during the eccentric portion
of gait to widen the support base with each step. They also assist in plantar flexion of the proximal phalanges, an important factor in the propulsion phase of gait. Furthermore, their proximal origins help keep the metatarsals from spreading too far apart and help maintain the transverse curvature of
the foot.

THE THIRD PLANTAR LAYER

The flexor hallucis brevis originates from the cuboid and the two lateral cuneiforms and inserts on the medial and lateral aspects of the proximal phalanx of the great toe via two tendons. It creates plantar flexion of the metatarsophalangeal joint (the proximal phalanx of the great toe).

The adductor hallucis has two origins: One is located obliquely from the bases of the second, third and fourth metatarsals; the other is located transversely from the capsules of the third, fourth and fifth metatarsophalangeal joints. Its tendon merges with the lateral tendon of the flexor hallucis brevis and inserts laterally on the base of the proximal phalanx of the great toe. The adductor hallucis creates adduction and dorsiflexion of the great toe. It is also the muscle primarily responsible for “hallux valgus,” an abnormality in which the first metatarsal is permanently abducted and the first proximal phalanx is adducted: In other words, the great toe overlaps the second toe.

Push-off at the great toe initiates the final dorsiflexion action of gait. Therefore, weakening of the muscles in the great toe can also create a poor push-off pattern and lead to dysfunction or pain that can travel up the body and cause joint misalignment up the
kinetic chain.

The final muscle in the third plantar layer is the flexor digiti minimi brevis. This muscle originates at the base of the fifth metatarsal and inserts on the base of the fifth proximal phalanx. It creates plantar flexion of the fifth toe.

THE SECOND PLANTAR LAYER

The muscles of the second plantar layer create movement and provide stability in the metatarsophalangeal, distal
interphalangeal and proximal interphalangeal joints.

The lumbricals are four small muscles originating at the tendons of the flexor digitorum longus and inserting on the dorsal parts of the tendons of the extensor digitorum longus. They work with the interossei to create plantar flexion of the interphalangeal joints when the metatarsophalangeal joints are held in flexion. This happens during the propulsion phase of gait, when the toes push off the ground.

The quadratus plantae has two origins: Its medial head originates at the medial surface of the calcaneus; its lateral head originates at the lateral aspect of the inferior surface of the calcaneus. This muscle inserts on the posterolateral border of the tendon of the flexor digitorum longus. Together with the flexor digitorum longus, the quadratus plantae creates flexion of the distal interphalangeal joints. It redirects the pull of the flexor digitorum longus tendons so they are more in line with the axes of the toes.

THE FIRST PLANTAR LAYER

The first plantar layer of foot muscles, the most extrinsic plantar layer, creates action of the toes.

The abductor hallucis originates at the calcaneus and medial flexor retinaculum, inserts medially on the base of the proximal phalanx of the great toe and plays an important role in keeping the great toe aligned by preventing hallux valgus. It also aids abduction and plantar flexion of the great toe.

The flexor digitorum brevis originates at the posteroinferior tuberosity of the calcaneus, splits into four parts and inserts laterally on the middle phalanges of the second, third, fourth and fifth toes. This muscle creates plantar flexion of the middle and proximal phalanges of those toes. When the interossei are weak, this strong muscle often creates “clawfoot,” a condition in which the middle phalanges pull back and lift in a phasic state.

Finally, the abductor digiti minimi originates at the posteroinferior calcaneus and inserts laterally on the base
of the fifth proximal phalanx. It creates abduction of the fifth toe and supports the lateral arch of the foot.

Dynamics of Foot Movement

In addition to dorsiflexion and plantar flexion at the ankle, the foot can move about the vertical axis of the leg and about its own horizontal and longitudinal axes. This is where adduction and abduction (vertical axis), supination and pronation (longitudinal axis), and inversion and eversion (horizontal axis) occur.

The distal tibia and fibula form the medial malleolus and lateral malleolus respectively and articulate with the dome of the talus to create the foundation of the ankle joint. Just beneath the talus is the calcaneus, the most posterior and massive bone in the foot. Both the talus and the calcaneus articulate to form the subtalar joint.

No muscles insert on the talus. This bone is supported and moved indirectly via the structures surrounding
it. The talus also articulates with the
navicular to create the talonavicular joint, involved in movements ascribed to the subtalar joint.

Supination and pronation are movements permitted by the subtalar and talonavicular joints. Supination is rotation of the foot in which the sole moves in a medial direction. Pronation is rotation of the foot in which the sole moves in a lateral direction. Attaching to the inferior calcaneus and along the plantar surface of the foot and splitting into five slips that attach to the toes is the plantar aponeurosis, a thick layer of fibrous tissue that contributes to the arches of the foot. On the calcaneus is the sustentaculum tali, a prominent projection that supports the talus and provides a passage-like groove for various tendons, blood vessels and nerves. This is also the insertion area for the Achilles tendon.

The articulations of the talus with the navicular and the calcaneus with the cuboid form the transverse tarsal joints, which permit adduction (movement in a medial direction) and abduction (movement in a lateral direction) of the forefoot. In discussing adduction or abduction of the toes, the reference is not the median plane of the body but the axis of the second toe. When the knee is extended, these movements are often confused with medial and lateral rotation of the hip. They are also confused with rotation of a flexed knee. Adduction and abduction of the foot originate at the subtalar joints; the ankle joint is purely a hinge joint.

Inversion, a combination of supination and forefoot adduction, is more easily achieved when the foot is in plantar flexion as well. Eversion, a combination of pronation, dorsiflexion and forefoot abduction, is more
attainable in dorsiflexion than in plantar flexion.

Reinforce the Foundation
of the Body

To correct misalignments beginning
at your client’s foot, implement a program designed to work your client out of his shoes. (See “Suggested Exercises” on page 48.) Such training may not
be “sexy,” but knowing how to maintain the basic structural components
of the foot can help correct other extraneous misalignments up the chain of the body.

THE FOOT MUSCLES: ORIGIN, INSERTION AND ACTION

SUGGESTED EXERCISES

The following exercises increase joint motion in the feet and strengthen the intricate muscles that control foot motion. They also foster more accurate articulation of foot placement to utilize the full range-of-motion (ROM) potential in walking or standing.

1. Basic Foot Challenge

2. Heel Circles and Parabolas (Foot Movement Awareness)

3. Foot Rocking

The following three exercises are not very exciting but are effective at strengthening the muscles of both the lower leg and the foot. They use a towel spread out on the floor in front of a chair, and one performs them while seated on a chair so the knees and hip joints are at 90-degree angles. The feet should be flat on the floor. (Unlike a rug or carpet, a hardwood floor makes it possible to move the towel without resistance.)

Again, watch for deviations or faulty recruitment patterns. You can modify these exercises by first assisting and resisting the client’s movements with either your hands or a Thera-Band and then advancing to the towel-curling series. If providing manual assistance, you should stabilize the heel of the exercising foot with one hand while using the other hand
as resistance in the movement. If you use a Thera-Band for resistance, it is still a good idea to use one hand to secure the heel for better, more specific movement in the foot. The Thera-Band can be knotted at one end
to create a loop to perform exercises more efficiently.

The client should perform each exercise with one foot at a time and complete a 10-repetition maximum before switching feet. In addition, you can make these exercises more challenging by putting weight on the towel for the client to pull.

4. Arch Strength

5. Supination/Inversion

6. Pronation/Eversion

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