hip adductors(also called leg adductors) are the inner muscles of the leg that help in bringing the leg closer to your mid-line. pectineus, adductor longus, gracilis, adductor brevis, and adductor magnus(which contains adductor minimus as well) are the main muscles that help with that action. also they are muscles in your medial hamstring(semitendinosus and semimembranosus) and medial quadriceps(vastus medialis) which help in a small degree in that process as well. most gyms have a seat for adductor training but the fact is because you are sitting on the muscle you are training, that can affect your training in a bad way by causing a lot of pressure to the contracted muscle and also stretching the hamstring and reducing the range of movement. also most the hip adductor machines work with a bent knee. some muscles mentioned above cross the knee and it is not a good practice to train them with a bent knee.