What is the primary muscle group being stretched during a hip flexor stretch?

The primary muscle group being stretched during a hip flexor stretch is indeed the iliopsoas. This muscle group, which includes the psoas major and iliacus muscles, is located in the hip region and plays a crucial role in hip flexion as well as stabilizing the pelvis during activities like walking and running.

When performing a hip flexor stretch, the position typically involves extending the hip while keeping the knee bent, which targets the iliopsoas by increasing the distance between its attachments on the femur and the lumbar spine. This positioning effectively elongates the iliopsoas, helping to relieve tension and improve flexibility in this area.

In contrast, the other muscle groups listed, such as the hamstrings, quadriceps, and pectorals, are not primarily involved in or affected by a hip flexor stretch. The hamstrings are more involved in hip extension and knee flexion, the quadriceps are primarily responsible for knee extension, and the pectorals are located in the chest region, unrelated to hip movements. Thus, the iliopsoas is the focal point of the stretch, making it the correct answer.