Horizontal grooves in the forefoot of running shoe midsoles are called flex grooves. As the name implies, flex grooves are designed to promote forefoot flexion across the metatarsophalangeal joints (MPJs).
In many cases of forefoot pain, however, this is exactly where you don’t want the shoe to bend. You actually want the shoe to be as inflexible as possible in this area when patients have hallux limitus, sesamoiditis and lesser MPJ capsulitis or predislocation syndrome.
When patients have these conditions, deep flex grooves located directly beneath the affected joint will cause an increase in MPJ plantarflexion as well as reduced shock absorption due to a lack of an overlying outsole in the area of a groove.
The shoe (on the left side of the photo) shows a flex groove distal and proximal to the plantar MPJs, which is better for forefoot pain. The shoe on the right side of the photo shows a flex groove directly plantar to the MPJs.
If you have a patient with metatarsalgia who wears athletic shoes for workouts or substantial walking, you will want to check the placement of the shoes’ flex grooves and advise accordingly.