**Question:** Flexors of lumbar spine are all EXCEPT:

A. Erector spinae
B. Multifidus
C. Transversus abdominis
D. Internal oblique

**Core Concept:**

The lumbar spine is a part of the spinal column that supports the body's weight and aids in various movements, including flexion. The lumbar spine has several muscle groups responsible for its movement, including flexion. In this question, we are looking for a muscle group that is not involved in flexion.

**Why the Correct Answer is Right:**

The correct answer, D. Internal oblique, is not involved in lumbar spine flexion because it primarily functions in rotation and lateral flexion movements. The other options are involved in lumbar spine flexion:

A. Erector spinae: These muscles extend the spine but can also contribute to flexion when contracted simultaneously with flexor muscles.
B. Multifidus: This muscle extends and stabilizes the spine but can also contribute to flexion when contracted simultaneously with flexor muscles.
C. Transversus abdominis: Although this muscle is primarily involved in abdominal wall stabilization, it can also contribute to lumbar spine flexion when contracted simultaneously with the flexor muscles.

**Why Each Wrong Option is Incorrect:**

A. Erector spinae: Although erector spinae contributes to lumbar spine extension, it can also be involved in flexion when contracted simultaneously with flexor muscles.
B. Multifidus: Similar to erector spinae, multifidus is involved in lumbar spine extension but can also contribute to flexion when contracted simultaneously with flexor muscles.
C. Transversus abdominis: As mentioned earlier, transversus abdominis is primarily involved in abdominal wall stabilization but can contribute to lumbar spine flexion when contracted simultaneously with flexor muscles.

**Core Concept:**

The lumbar spine flexion is primarily achieved through the contraction of flexor muscles. When these muscles contract together, they can also cause extension and stabilization of the spine.

**Clinical Pearls:**

1. In clinical practice, understanding muscle function in lumbar spine flexion is essential for treating patients with back pain or spinal movement issues. A thorough understanding of muscle anatomy and function allows for proper diagnosis and treatment planning.
2. When assessing patients with spinal movement issues, examining the function of the flexor muscles, including the erector spinae, multifidus, and transversus abdominis, is crucial for determining the cause of the patient's symptoms and developing an appropriate treatment plan.

**Why the Correct Answer is Right:**

The internal oblique abdominals (option D) is not involved in lumbar spine flexion and is not considered in the context of spinal movement.

**Why Each Wrong Option is Incorrect:**

A. Erector spinae: Although erector spinae contributes to lumbar spine extension, it does not have a primary role in flexion.
B. Multifidus: Similar to erector spinae, multifidus is primarily involved