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  • Foot Anatomy and Biomechanics
    Tibialis Posterior, Peroneus Longus, Peroneus Brevis and Tibialis Anterior

    A basic foot exercise involves rolling the shins out and pressing down through the outer edge of the foot while also pressing down through the inner edge of the forefoot (and optionally creating an upward pull on the center of the outer arch of the foot).

    Side view of fibula and tibia and foot showing peroneus longus and tibialis anterior muscles as well as the bottom end of the IT band. Neil Keleher. Sensational Yoga Poses.

    The foot muscles involved in this foot exercise include:

    i Tibialis Posterior

    The primary action of rolling the shins out while standing is caused by Tibialis Posterior.

    Note that rolling the shins externally can also be caused by the muscles that act on the IT Band.

    However, if the focus is on "using the feet" to roll the shins out, then this action can be driven by activation of the Tibialis Posterior.

    You may feel tension in the back of your lower leg while rolling your shins out. That could be your tibialis posterior activating.

    Tibialis Posterior Connections

    Tibialis Posterior attaches to the backs of both the fibula and tibia. Its tendon passes down the inside of the ankle to attach to the underside of the inner arch of the foot.

    Tibia and fibula side view along with bones of the foot and the two muscles Tibialis Posterior and Tibialis Anterior. Neil Keleher. Sensational Yoga Poses.

    More specifically, it passes behind the Medial Malleolus (but in front of the sustentaculum tali which is a projection on the inside of the calcaneus or heel bone.)

    Its main branch attaches to the Medial Tubercle of Navicular, which you can feel just forward of and below the medial malleosus and to the bottom surface of the inner most (medial) cuneiform.

    Another set of branches attaches to the underside of the cuboid, the two outer most cuneiforms and to rearmost parts of the undersides of metatarsals 2, 3 and 4 ( the bones that attach to the middle three toes).

    Another branch of the tibialis posterior reaches back to attach to the sustentaculum tali as it passes it.

    Because it passes behind the medial malleosus (the bottom of the tibia), when activated it creates a forward pushing force on the inside of the tibia which can cause an external rotation.

    Because of its attachment to the sustentaculum tali, when activated, tibialis posterior pulls upwards on the inside surface of the calcaneus (the "heel" bone).

    It also pulls backwards and upwards on the inner surface of navicular.

    And it creates a backwards pull on the base of the cuboid, the cuneiforms and the three middle of the foot metatarsals.

    While standing, these forces from an activated Tibialis Posterior can all together can lift the inner arch of the foot and at the same time roll the shins outwards.

    Or more subtly, they can resist the arch collapsing and the shin from rolling inwards.

    i Peroneus Longus

    Peroneus longus attaches to the outside of the fibula (the outermost and smallest of the two lower leg bones.)

    Side view of fibula and tibia and foot showing peroneus longus and tibialis anterior muscles as well as the bottom end of the IT band. Neil Keleher. Sensational Yoga Poses.

    It passes down the outside of the ankle behind the Lateral Malleolus (the bottom most part of the fibula, that sticks out of the outside of the ankle) and passes under the foot to attach to the inner arch and to the "root" of the big toe.

    More specifically, this muscle passes behind the Trochlear Process (or Peroneal Tubercle) of the calcaneus. (You may be able to feel this protrusion of bone just below and in front of your lateral malleolus.)

    From there it passes along the outside of the cuboid and then folds around that bone to pass inwards and forwards, through a canal along it's underside. It passes diagonally along the underside of the outermost two cuneiforms before attaching to the underside of the innermost cuneiform and to the rearmost part of the base of the innermost metatarsal.

    Assuming a standing position, (which means that the feet are being pushed down by the weight of the body) and assuming that the tibialis posterior is already activated and so resisting inward rotation of the shin , the peroneus longus can act from a stabilized fibula.

    It can create an upwards and inwards pull on the outside arch of the foot (as it passes under cuboid). And it can create a backwards pull at the peak of the inner of the foot where it attaches to the innermost cuneiform and metatarsal.

    Acting in concert with the tibialis posterior, the peroneus longus can help shape the inner and outer arches of the foot.

    The Tibialis Posterior and Peroneus Longus Working Together to Stabilize the Heel

    Note that because it passes behind and under the trochlear process (peroneal tubercle) on the outside of the calcaneus, Peroneus Longus tends to create a forwards on the outside edge of the calcaneus which, unresisted, would cause the heel bone to roll inwards. This may be resisted by an active tibialis posterior since this muscle has a branch that attaches to the sustentaculum tali on the inside edge of the calcaneus.

    The action of both muscles together then not only help to form the inner and outer arches of the feet, they can also help to stabilize the heel laterally, preventing it from wobbling from side to side.

    Creating Rotational Stability via Co-activation of the Tibialis Posterior and The Peroneus Longus

    Where activation of the tibialias poster tends to create external rotation of the shin (or a resistance to internal rotation), activation of the peroneus longus (and/or peroneus brevis) can tend to create internal rotation of the shin (or a resistance to external rotation.

    Activating together, these two muscles can work against each other to stabilize the shin against rotation while standing.

    This can be important for muscles that act on the IT Band as well as the Sartorius, Gracilis and Semitendinosus muscles since these muscles can act from the pelvis to rotate the shin outwards or inwards. With the shin stabilized against rotation by the Tibialis Posterior and Peroneus Longus, these muscles have a stable foundation from which to help control the pelvis.

    i Peroneus Brevis

    Peroneus Brevis, like Peroneus Longus, attaches outside of the fibula.

    Side view of fibula and tibia and foot showing peroneus brevis and tibialis anterior muscles as well as the bottom end of the IT band. Neil Keleher. Sensational Yoga Poses.

    It attaches to the lower part of the fibula underneath the peroneus longus. It passes down the outside of the calcaneus in front of the trochlear process (otherwise known as the peroneal tubercle).

    (The peroneus longus passes behind this bony projection.)

    Peroneus Brevis then passes along the outside of the cuboid before it attaches to the outer edge of the rearmost part of the outermost metatarsal. It's activation while standing creates a backwards and slightly upwards pull at the top of the outer arch of the foot.

    Recall that activation of the peroneus longus can create a forwards push along the outside of the calcaneus. Meanwhile the peroneus brevis creates a rearwards pull on the outer-most metatarsal.

    These opposing actions can work together to help lift the center of the outer arch of the foot.

    i Tibialis Anterior

    Tibialis Anterior is situated at the front of the shin.

    Medial (inside) view of and tibia (and fibula) and foot showing tibialis anterior muscle. Neil Keleher. Sensational Yoga Poses.

    Medial/Inside View

    Lateral (outside) view of fibula and tibia and foot showing tibialis anterior muscle. Neil Keleher. Sensational Yoga Poses.

    Lateral/Outside View

    It attaches to the front of the tibia outside of the tibia, starting high up, where the bone swells to form the bottom of the knee. It passes under the extensor retinaculum, a band of connective tissue at the front of the ankle. From there it runs along the inside edge of the upper surface of the foot to attach to the top surface of the inner most cuneiform and the rearmost part of the top surface of the innermost metatarsal.

    Recall that the peroneus longus attaches to the underside of this same bone (the innermost metatarsal).

    While the body is upright and with the feet bearing weight, and with the peroneus longus activated to resist the any upward pulling of the innermost metatarsal, the tibialis posterior is anchored so that it can act on the tibia. Because it attaches towards the outside of the tibia, it may tends to try to internally rotate the tibia, assuming the innermost metatarsal is stabilized against it's pull.

    So the Tibialis Anterior and Peroneus Longus can act in concert to resist the internal rotation effort caused by an active tibialis posterior.

    Tibialis Anterior as a Fascial Anchor for the IT Band

    From Thomas Meyers Anatomy Trains we know that the Tibialis anterior has a connective tissue connection to the front fibers of the IT band.

    (The rear edge of the IT band has connective tissue connections to the Peroneus Longus).

    Tension in the Tibialis anterior (and/or the Peroneus Longus) can act as an anchoring mechanism for the IT band so that it it turn can act as an anchor for the Tensor Fascia Latae and/or the Gluteus Maximus.

    For myself, on one occasion where I had knee pain pretty much at the spot where the IT band connects to the Tibia, Tibialis Anterior activation helped to alleviate that knee pain.

    This sort of muscle activation, activating muscles in the same "anatomy train" is another way of creating stability. Possible names for this mechanism are "Fascial Stability" or "Fascial Anchoring" or to be clearer, "Muscle Activated Connective Tissue Anchoring."

    It's basically a means of taking up slack.

    It creates stability for a muscle by adding tension to the connective tissue structure that it is a part of.

    Stabilizing the Foot and Shin

    The actions of all of these muscles, acting in concert, can not only help shape and stabilize the arches of the foot, they also help to stabilize the shins against rotation giving muscles like the tensor fascia latae, gluteus maximus, sartorius, gracilis and semitendinous a stable foundation from which to control or help stabilize the pelvis.

    The muscles can activate to stabilize the foot with the arches nicely formed, but they can also activate to stabilize the foot, ankle and shin with the arches "collapsed", or any position in between.