An interesting biomechanical issue unpacked this week.
In our performance enhancement session with a runner, we were discussing foot biomechanics and past injuries. These included tibial stress fractures, navicular fractures, tight calves and plantar fasciitis.
Looking at the foot there was a degree of (more than normal) overpronation, leading to a lack of use of the windlass mechanism. This is where the big toe flexes and tightens the plantar fascia, making the foot into a rigid lever. This allows a firm surface to push off. Lack of use of the windlass means the foot is less rigid, and a firm base for propulsion is not available. Consequently, the calves are having to work harder than normal to provide a propulsive force. This is one reason calves tighten up when running.
Overpronation and tight calf can cause a functional elongation of the plantar fascia and bowing of the Achilles tendon, which can lead inflammation at the tendon insertion and tendinosis. At the calcaneal insertion of the fascia, it can cause plantar fasciitis.
Stiff Big Toe
In addition to overpronation, the foot had a reduction in flexion of the big toe. The effect of reduced range of flexion at the big toe continues up the biomechanical chain. It prevents the hip from extending fully, reducing the elastic recoil of hip structures. Along with the associated issues; reduces extensor power, encouraging hip flexors to pull through rather than hip extensors to push off. The over worked hip flexors become tight, causing anterior hip pain. Also, due to their attachment on the anterior surfaces of the five lumbar vertebrae, tight hip flexors can lead to hyperextension in running and low back pain.
The human body is a kinetic chain. What happens at one joint will have a knock on effect at another joint.Correcting the overpronation and mobilising the big toe joint, allowed the higher biomechanical chain to be more effective and reduced stress and strain through the lower limb, solving a number of recurring issues in one go!