Which muscles are major contributors to the deep longitudinal sub-system?

The deep longitudinal sub-system primarily involves a combination of muscles and connective tissues that play a crucial role in the stabilization and functional movement of the spine and lower extremities. The muscles listed in the correct answer—erector spinae, thoracolumbar fascia, sacrotuberous ligament, and biceps femoris—are intricately linked in how they support and facilitate movement.

The erector spinae group of muscles contributes significantly to spinal extension and maintaining an upright posture. The thoracolumbar fascia serves as a connective tissue structure that connects these muscles, providing stability and support to the lumbar region. The sacrotuberous ligament connects the sacrum to the ischial tuberosity, enhancing the stability of the pelvis and lower back during dynamic activities. The biceps femoris, a part of the hamstring group, not only aids in knee flexion but also plays an important role in hip extension and stabilization of the pelvis, which is vital for maintaining balance and posture in movement patterns.

This combination of muscle and connective tissue is essential for the efficient transfer of forces through the body, particularly during activities that require coordinated movement of the upper and lower limbs, hence their classification in the deep longitudinal sub-system.