Semimembranosus – Anatomy Breakdown

Nov 11

Treadwell, DPT | Muscle by Muscle Series

Watch the Episode

Watch on YouTube: Semimembranosus – Anatomy Breakdown

In this episode, Dr. Austin Treadwell, DPT breaks down the Semimembranosus — the deep, broad hamstring that holds the medial side of your posterior chain together.
It’s not flashy, but it’s critical — especially for pelvic stability, knee control, and injury prevention.

This is a thumbnail for the Semimembranosus anatomy video by Austin Treadwell, DPT covering origin, insertion, action, innervation, and clinical tidbits

Overview

The Semimembranosus is the deepest and most medial of the three hamstrings.
It sits just beneath the Semitendinosus, running from the ischial tuberosity down to the posterior medial tibia.
While the Semitendinosus handles range and leverage, the Semimembranosus provides stability and control — think structure, not show.

Clinically, it’s a major stabilizer for the posteromedial knee and a frequent site of chronic hamstring strain or postural imbalance.
In athletes, underdeveloped Semimembranosus strength can contribute to hamstring asymmetry and ACL vulnerability.

Origin & Insertion

Origin: Ischial tuberosity (upper lateral facet)
Insertion: Posterior aspect of the medial tibial condyle, forming expansions to the oblique popliteal ligament and joint capsule

Its wide, membranous tendon explains the name — and its connections to the joint capsule make it a true stabilizer, not just a mover.

Function

Primary: Hip extension, knee flexion, and tibial internal rotation (when knee flexed)
Secondary: Reinforces posterior knee capsule and assists in pelvic control

EMG imaging and MRI studies show the Semimembranosus is most active in the terminal swing and early stance phases of gait, providing eccentric control and dynamic joint stabilization (Higashihara et al., 2024).

It works closely with the Semitendinosus and Adductor Magnus to manage medial stability and coordinate hip drive.

Innervation & Blood Supply

Innervation: Tibial division of the sciatic nerve (L5–S2)
Blood Supply: Perforating branches of the deep femoral artery

Clinical & Training Insights

Proximal tendinopathy of the Semimembranosus is common in distance runners and field athletes — often mistaken for “high hamstring” pain.
The oblique popliteal ligament connection makes this muscle key for posterior knee stability — don’t skip it in knee rehab.
Use eccentric hip-extension drills (RDLs, Nordic variations) and isometric holds at mid-range to target its deep stabilizing role.
Post-ACL reconstruction, restoring Semimembranosus function supports rotational control and reduces re-injury risk.

Clinical note: Chronic Semimembranosus stiffness can contribute to posterior pelvic tilt and reduced hip extension drive — often a hidden limiter in speed and stride efficiency.

Clinical Relevance

The Semimembranosus is the quiet stabilizer of the posterior chain.
It reinforces medial knee alignment, coordinates hip extension with pelvic control, and serves as a cornerstone in both hamstring injury prevention and knee rehabilitation.
When it’s underactive, expect overcompensation from the low back, glutes, or lateral hamstrings.

Take the Next Step

You’ve got the anatomy down — now put it into motion.
If you’re a clinician, let’s talk posterior knee stability and hamstring rehab.
If you’re an athlete or lifter, let’s talk hip extension, sprint power, and injury prevention.
And if you’re rehabbing an old hamstring strain — this is where anatomy meets recovery.

𖤓 Watch more breakdowns on YouTube: Treadwell, DPT – Muscle by Muscle Series
𖤓 Book a Virtual Consultation: TreadwellDPT.com/appointments
𖤓 Download free PT tools & anatomy resources: TreadwellDPT.com/resources

Much more in store; even more to come.
Stay tuned, stay locked. Treadwell, DPT. 🏹

Austin Treadwell