Longus also acts like a bowstring that braces the transverse arch of the foot.

Under the foot, the longus stretches from the lateral to the medial side in a groove, thus bracing the transverse arch of the foot.

It is one of the 3 ligaments responsible for maintaining the transverse arch of the foot together with the interosseous ligaments of metatarsals and the transverse metatarsal ligament.

Direct pressure between the metatarsal heads will replicate the symptoms, as will compression of the forefoot between the finger and thumb so as to compress the transverse arch of the foot.