02/15/2026
I love this account. Look at how the hamstrings connect to the sacrum. Now think about how tight hamstrings would inhibit sacral movement, and how a supple posterior chain (relaxed calves and hamstrings) would support sacral movement during birth!
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Hamstrings, Sacrotuberous Ligament & SI Joint: A Hidden Biomechanical Link
This image highlights a powerful but often overlooked anatomical connection between the hamstrings, sacrotuberous ligament, and the sacroiliac (SI) joint complex. What looks like separate structures actually function as a continuous myofascial and ligamentous system that plays a major role in pelvic and spinal stability.
On the left, the superficial dissection shows how the hamstrings blend into the posterior thigh fascia and connect upward toward the pelvis. Rather than ending only at the ischial tuberosity, the hamstring fascia integrates with the sacrotuberous ligament, forming a strong tension-transmitting structure between the femur and sacrum.
The deeper dissection on the right reveals that the tendon of the long head of biceps femoris directly connects into the sacrotuberous ligament, which then blends with the SI joint ligaments. This means hamstring tension can directly influence sacral position and SI joint mechanics. Increased hamstring tone can increase tension across the SI joint, affecting load transfer between the trunk and lower limb.
Biomechanically, this connection is crucial during activities like walking, running, bending, and lifting. When the hamstrings contract, they donât just extend the hipâthey also contribute to force closure of the SI joint, enhancing pelvic stability. However, excessive stiffness or asymmetry in the hamstrings can overload the sacrotuberous ligament and contribute to SI joint pain or dysfunction.
Clinically, this explains why hamstring tightness is often associated with low back pain, pelvic pain, or SI joint symptoms. Treating the hamstrings alone without considering their sacral and fascial connections may provide only temporary relief.
The hamstrings are not just knee flexors or hip extensorsâthey are integral stabilizers of the pelvis and SI joint. Understanding this anatomical continuity helps clinicians and movement professionals address pain, posture, and performance more effectively by treating the entire lumbopelvic system, not isolated muscles.