What is the primary action of the psoas muscle at the hip joint?

The psoas muscle primarily functions as a hip flexor. Its anatomical position allows it to effectively bring the thigh toward the torso, which is the key movement in hip flexion. This action is crucial not only for walking and running but also for many Pilates exercises that require a connection between the upper and lower body.

The psoas, which originates from the lumbar vertebrae and attaches to the lesser trochanter of the femur, plays a significant role in stabilizing the spine and pelvis while facilitating leg movements. This stabilizing aspect is particularly important in Pilates, as many exercises emphasize core strength and alignment while engaging the hip flexors.

In contrast, the roles of extensor, abductor, and adductor do not accurately reflect the primary action of the psoas muscle. Extensors are responsible for moving the thigh backward, abductors move the thigh away from the midline of the body, and adductors bring the thigh back toward the midline; none of these actions are characteristic of the psoas muscle's primary function during hip joint movement.