A sole structure includes a sole plate having a foot-facing surface with a forefoot portion, and a ground-facing surface opposite from the foot-facing surface. The sole plate includes a plurality of grooves extending transversely relative to a longitudinal axis of the sole plate, in the forefoot region of the foot-facing surface. A flex control insert includes an upper surface, and a lower surface opposite the upper surface. The flex control insert includes a plurality of ribs protruding from the lower surface of the flex control insert, which extend transversely relative to the longitudinal axis of the sole plate. Each one of ribs is disposed within a different respective one of the grooves. The ribs are strong in compression, and maintain their volume to resist compression by the grooves as the sole plate flexes in a longitudinal direction to increase the bending stiffness of the sole plate.