Which muscle does NOT assist in flexing the hip joint?

The gluteus maximus is primarily involved in hip extension rather than hip flexion. While it does have some role in stabilizing the hip and assisting with activities that require movement of the hip joint, its major action is to extend the hip, especially when moving from a flexed position to an upright position, such as when rising from a seated position or during activities like running and jumping.

In contrast, the psoas, pectineus, and tensor fascia latae are all muscles that contribute to hip flexion. The psoas is a major flexor of the hip and plays a critical role in lifting the thigh upward and stabilizing the pelvis. The pectineus assists with flexing the hip as well, while the tensor fascia latae helps in flexing and abducting the hip. Understanding the functions of these muscles helps clarify why the gluteus maximus does not assist in flexing the hip joint, as it has a contrasting primary function.