Final answer:
Resisting the patient's effort to flex, abduct, and externally rotate from a seated position tests the strength of the hip abductors, particularly the gluteal group of muscles including the gluteus maximus, medius, and minimus.
Step-by-step explanation:
A test that involves a seated position, resisting the patient's effort to flex, abduct, and externally rotate primarily evaluates the strength of the hip abductors.
In more detail, from a seated position, when a patient tries to flex the hip, they engage the iliopsoas group, which raises the knee at the hip. This group also assists with twisting the thigh outward in external rotation. However, the act of abduction, wherein the leg moves away from the midline of the body, specifically tests the gluteal group which includes the gluteus maximus, medius, and minimus that extend and abduct the femur at the hip.
The gluteal group is closely associated with these motions, in cooperation with muscles like the piriformis and the tensor fascia lata, which also contribute to lateral rotation of the thigh and stabilization during abduction.