A number of factors can cause arch pain. The plantar fascia, peroneus longus, flexor digitorum, hallucis tendons, and abductor hallucis, just to name a few.
The most common mid-arch pain often involves the peroneus longus tendon. This tendon originates on the lateral (outside) of the leg and runs down past the lateral ankle bone. It passes the styloid process at the base of the fifth metatarsal, under the foot and inserts at the base of the first metatarsal ray in the middle of the arch.
The peroneus longus maintains the integrity of the arch, pulling the first ray down, re-establishing the arch prior to heel lift off. Essentially it has an anti-pronation function.
When the foot is forced into excessive pronation due to structural alignment or muscle imbalances, the first metatarsal ray will be forced to dorsiflex upward, which strains the peroneus longus.
Depending on the level of activity, runners often get this, and other people who are on their feet a lot. Also, people who simply pronate too much. Arch pain often goes hand in hand with bunion development, dorsal exostosis, or mid-foot joint pain.
Treatment involves identifying the biomechanical causes of why the arch is under pressure to pronate. Providing stretching exercises, foot mobilisation, soft tissue mobilisation and Compex (neuromuscular electrical stimulation) and insoles or orthotics where necessary.