If your Tibialis Posterior (TP) is weak, what kinds of performance and health issues can you get? It’s a major factor for foot pronation, plantar fascitis, achilles tendonitis, shin splints, knee pains and lots more. Let’s look at TP anatomy, actions, measurement methods along with the implications weak TP strength can have on your athletic performance and health.
Anatomy – The TP muscle is located in the back of your calf region. The top of the muscle attaches to the top and back of the tibia and fibula bones as well as the tough membrane that lies between them. The muscle runs down the back of the calf, connects to its’ long tendon which runs behind the medial ankle. From there, the tendon continues around the mid foot at about the peak of the long foot arch. There it breaks up into many smaller tendons which attach to the bottom of most of the bones in the mid foot.
Action – The main action of this muscle will be to flex your foot to the bottom (plantar flexion) and twist the forefoot medially (inversion). The quick way to refer to this motion is that it twists your foot down & in. This is one of the key ‘stabilizing’ muscles of the foot. In addition to twisting your foot down and in, the TP is also one of the primary muscles holding up the long arch of the foot.
Diagnosis – Weakness in the TP can be determined with manual muscle strength testing, careful observation of ankle movement during walking, running and at rest, long arch height measurements and other tests. Supporting information can be gained through a careful history as well as physical examination for neurological, vascular and orthopedic signs. Detailed measurement of TP ranges of motion and muscle strength are available with specialized equipment when required for insurance purposes, research or in advanced cases.
Functional Implications – When the TP muscle is weak, you will not have the strength you should when a) moving the forefoot down & in, b) your ankle will be unstable and c) there will be some degree of difficulty holding up your long arch (excessive foot pronation) when the foot is put under more stress than the muscle can handle. In more advanced weaknesses, the foot will be unable to hold the long arch up during even mild stress such as weight bearing. With extreme or prolonged weakness, the long arch may become permanently deformed to the flat position (flat footed) even without weight bearing.
Performance Issues (Arch) – Difficulty in holding up the long arch will have implications in a very large number of sports. Any athlete involved in sports which include running will suffer to some degree. If the long foot arch is fully collapsed, shock absorption will be reduced (depending on what type of foot strike you use). Speed will be lost as the forefoot cannot contribute as effectively in the toe off phase.
Performance Issues (Knee) – When the ankle pronates, the long arch collapses medially. If you stand and look at your knee while you pronate your foot, you will see that this motion also results in the knee deviating medially (towards ‘knock kneed’). This stretches the medial collateral ligament and strains one of the thigh adductor muscles (the gracilis).
Athletes in sports that require high power outputs in the legs (such as weight lifting and high jumping), with weak TPs, may notice that their knees ‘give out’ or ‘buckle’ medially when under high stress. When joints buckle outside of their normal ranges of movement, reflexes are initiated which severely restrict continued muscle contraction. A weak TP can effectively become the weak link which limits your athletic performance.
Athletic Performance Issues (Down & In) – Sports that use the motion of twisting the foot down and in will suffer when this muscle is weak. Kicking a soccer ball in a forward / diagonal direction is a clear example. While the main power behind the kicking is due to the larger thigh muscles, additional power is also derived from the TP to give you the extra power needed to advance you to the next level of athletic performance. Perhaps more important than the extra power, will be the degree of ball control that is lost in kicking because the forefoot cannot maintain a reliably stable kicking surface.
Sports with jumping that include a lateral motion like basketball or volleyball will also suffer. Athletes who need agility with strong lateral movement will be aided by the TP to evade their competitors as in football.
Injury Susceptibility – In addition to performance degradation, athletes with weak TPs will be susceptible to increased rates of injury due to ankle and knee instability. Medial to lateral movement of the foot may be increased with each step. This will result in a few complications, including:
- Stretching the ankle ligaments that help maintain joint integrity against ankle sprains
- The achilles tendon will experience excessive movement at the ankle joint leading to potential achilles tendonitis
- The knee deviates medially each time the foot pronates. This leads to stretching of the medial collateral ligament of the knee, knee instability and a wide range of secondary issues.
Chronic Weakness – People who experience weak TP issues for many years are putting their feet and knees through excessive wear and tear that can eventually lead to cartilage damage, osteoarthritis and potential for surgery.