Secondary Actions of the Flexor Digitorum Superficialis: 2. Assists with flexion of the digits at the metacarpophalangeal joints. Agonists: Dorsal Interossei, Palmar Interossei, Lumbricals, Flexor Digitorum Profundus, Flexor Digiti Minimi. Antagonists: Extensor Digitorum, Extensor Indicis, Extensor Digiti Minimi.