Knee flexion The prime flexors of the knee joint are biceps femoris, semitendinosus and semimembranosus, whereas popliteus initiates flexion of the “locked knee” and gracilis and sartorius assist as weak flexors. Animation @muscleandmotion The Strength Training App #kneeflexion #hamstringstrength #hamstringsworkout #kneepain #osteopathy #muscleandmotion #physiotherapy #chiropractic #manualtherapy | Bradley Blair Osteopath