PT on the Net Research

Muscles and Their Effect on the Most Common Foot and Ankle Deviations

tbmm logo

The muscles described in the reference charts that follow play a vital role in helping prevent the two most common deviations of the foot and ankle area – overpronation and lack of dorsiflexion. They provide the strength and support necessary for transfer of the body’s weight during all weight bearing activities and also help the body create movement and propulsion. This is precisely why it is important to keep these muscles healthy and working properly. When they are negatively affected by musculoskeletal deviations, they cannot perform the crucial tasks for which they are designed. Consequently, structural deviations can become worse and everyday activities, such as walking, standing and exercising can become painful.

To illustrate the importance of the muscles in the foot and ankle, let’s take a look at what happens when a person is walking. During a normal gait cycle, the feet and ankles work together to help stabilize the body’s center of gravity and displace the weight of the body over the foot. This helps the person maintain an upright position and forward movement. As the person is walking, the heel of the foot comes in contact with the ground (the outside of the heel is the first part that connects with the ground). At this point in the gait cycle the ankle is inverted (i.e., the weight is on the outside of the foot/heel) and the foot is supinated (i.e., the medial arch is raised up). As weight is transferred forward in the foot during the gait cycle, the ankle rolls inward toward the midline of the body and the foot pronates (the medial arch flattens out slightly).

This action of pronation is pivotal in helping ensure the muscles of the feet and ankles activate like bungee cords as they lengthen. As the foot pronates, the muscles get more tension on them because the insertion points of these muscles (e.g., under the foot) move away from their points of origin (e.g., up on the lower leg). This stored energy is then used to help roll the foot back out (supinate) as is needed to complete the gait cycle correctly. Pronation only becomes problematic when the foot and ankle overpronate. When this happens, the stored energy in the bungee cord system of the muscles is lost due to the foot (and whole body) collapsing inward. Hence, it becomes difficult for the muscles to shift the weight of the body back to the outside of the foot to complete a proper gait cycle.

Here are two examples of how the action of specific muscles (tibialis anterior and tibialis posterior and the soleus and gastrocnemius) work together to affect both overpronation and dorsiflexion.

Example One: Tibialis Anterior and Tibialis Posterior

As the foot pronates when a person is engaged in a weight-bearing activity, the medial arch of the foot collapses slightly. This movement causes the insertion point of the tibialis anterior (under the foot) to pull away from its origin point up on the front of the tibia. This pulling motion causes the muscle to lengthen and the origin and insertions points to move away from each other. The lengthening of this muscle allows the foot to pronate correctly by supporting the medial arch of the foot. The tibialis posterior, which also inserts underneath the foot, runs up and across the back of the leg to its origin point high on the back of the tibia. As the foot pronates, it also causes this muscle to lengthen and the insertion and origin points to move away from each other. This also provides support to the medial arch of the foot, but because of its origin point on the back of the tibia, this lengthening of the tibialis posterior prevents the tibia from internally rotating too quickly over the foot. The actions of these two muscles help coordinate the timing of the internal rotation of the lower leg and ensure that the foot pronates at the right rate and does not overpronate. Since the movement of the tibia also affects the position and timing of the knee as it moves medially, these muscles also indirectly affect knee function (positively or negatively, depending on if they are working correctly).

Example Two: Soleus and Gastrocnemius

After the heel has made contact with the ground during the gait cycle, weight is transferred forward as the shin bones and knee move over the foot. This means that the top of the foot and the front of the shin move closer together (i.e., dorsiflex) as the ankle and knee bend. The soleus, which originates high on the back of the tibia, attaches to the back of the heel via the Achilles tendon. Hence, this muscle lengthens like a bungee cord as the knee and ankle bend. Similarly, the gastrocnemius, which originates on the bottom of the femur just above the knee and inserts to the back of the heel via the Achilles tendon, lengthens to control dorsiflexion as the knee straightens (i.e., when the leg travels behind the body into extension during gait).

If the other muscles of the foot do not lengthen correctly to prevent the foot from overpronating, then the foot and ankle collapse instead of coming forward (i.e., dorsiflex) over the foot as it should during the gait cycle. This causes weight to transfer more in an inward direction than a forward direction. The overpronation and lack of dorsiflexion that results leads to the joints of the foot/ankle complex becoming stressed because the muscles intended to protect them from excessive force are not doing their job correctly.