Semitendinosus – Anatomy Breakdown

Nov 7

Treadwell, DPT | Muscle by Muscle Series

Watch the Episode

Watch on YouTube: Semitendinosus – Anatomy Breakdown

In this episode, Dr. Austin Treadwell, DPT breaks down the Semitendinosus — the long, cord-like medial hamstring that keeps your stride smooth and your posterior chain firing.This one runs deep in both movement and rehab, bridging strength, stability, and symmetry from hip to knee.

Thumbnail for a Semitendinosus anatomy review video by Austin Treadwell, DPT covering origin, insertion, innervation, action, and clinical tidbits

Overview

The Semitendinosus is one of the three hamstring muscles — positioned medially beside the Biceps Femoris.
It’s long, fusiform, and built for control through range — contributing to hip extension, knee flexion, and tibial internal rotation.

Functionally, it’s more than a mover; it’s a stabilizer that keeps the pelvis, knee, and trunk in sync.
Clinically, its tendon (the “semi-t” you feel behind your knee) is commonly used in ACL grafts — a testament to its strength and structure.

Origin & Insertion

Origin: Ischial tuberosity (shared with the long head of the Biceps Femoris)
Insertion: Medial surface of the proximal tibia via the pes anserinus (with gracilis and sartorius)

The pes anserinus acts as a multi-muscle anchor, blending forces that stabilize the medial knee during dynamic activity — especially in deceleration and change-of-direction tasks.

Function

Primary: Hip extension, knee flexion, and tibial internal rotation (when knee is flexed)
Secondary: Posterior pelvic tilt and medial knee stabilization

MRI and EMG studies show the Semitendinosus activates strongly during mid-stance and late-swing phases of sprinting, with peak tension during eccentric knee control (Higashihara et al., 2024).

Because of its long tendon and internal rotation function, it’s especially valuable in cutting, landing, and deceleration drills.

Innervation & Blood Supply

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

Clinical & Training Insights

Semitendinosus strains often occur near the proximal tendon junction — especially in sprinting and explosive starts.
Strengthening through long-length loading (e.g., Nordics, RDLs, razor curls) enhances fascicle length and reduces re-injury risk.
The pes anserinus insertion plays a stabilizing role in valgus control — making this muscle essential in knee rehab and ACL prevention.
Post-ACL graft harvests from the Semitendinosus require specific retraining to restore medial hamstring function.

Clinical insight: Restoration of fascicle length via eccentric loading is directly linked to decreased strain recurrence (Timmins et al., 2016).

Clinical Relevance

The Semitendinosus anchors the medial side of your posterior chain.
Dysfunction here affects not only hamstring integrity but also pelvic control, knee stability, and gait efficiency.
Rehab should emphasize timing, coordination, and eccentric strength — not just raw power.

Take the Next Step

You’ve got the anatomy down — now put it into motion.
If you’re a clinician, let’s talk medial hamstring rehab and ACL graft considerations.
If you’re an athlete or lifter, let’s talk posterior-chain training and sprint resilience.
And if you’re battling hamstring tightness or re-injury — 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