Semitendinosus Muscle: Anatomy, Function, Location, and Injuries

Last updated: August 17, 2026
Evidence reviewed: NCBI Bookshelf/StatPearls, PubMed-indexed systematic reviews, peer-reviewed sports-medicine research, and international hamstring-injury consensus guidance.
Clinical review: This article has not been individually reviewed by a named clinician. It is educational only and is not a substitute for personal medical assessment, diagnosis, or rehabilitation advice.

The semitendinosus is a hamstring muscle at the back of the thigh. It works with the biceps femoris and semimembranosus to extend the hip and bend the knee. Its tendon is also a commonly used hamstring autograft source for anterior cruciate ligament (ACL) reconstruction 

The semitendinosus is a medial hamstring muscle in the posterior thigh. It originates at the ischial tuberosity and inserts on the medial proximal tibia through the pes anserinus. Its main actions are hip extension, knee flexion, and medial rotation of the tibia when the knee is bent 

Semitendinosus Anatomy Summary

Attribute	Detail
Origin	Ischial tuberosity
Insertion	Medial proximal tibia through the pes anserinus
Main actions	Hip extension, knee flexion, medial tibial rotation with the knee flexed
Innervation	Tibial division of the sciatic nerve
Blood supply	Perforating branches of the profunda femoris artery
Muscle group	Hamstrings; posterior thigh compartment
Key clinical relevance	Hamstring strain injury and ACL autograft harvesting

Source: StatPearls anatomy of the semitendinosus and posterior thigh

What Is the Semitendinosus Muscle?

The semitendinosus is one of the three main hamstring muscles, alongside the biceps femoris and semimembranosus. It is part of the posterior thigh compartment and is supplied by the tibial division of the sciatic nerve 

Its name reflects its long, narrow tendinous portion: semi means “half,” while tendinosus means “tendon-like.” A tendinous inscription divides the muscle belly into two segments, a feature visible on dissection and imaging.

The semitendinosus lies in the medial posterior thigh. The biceps femoris is lateral, while the semimembranosus lies deeper and more medial. Near the knee, the semitendinosus tendon travels toward the front and medial side of the proximal tibia.

Where Is the Semitendinosus Located?

The semitendinosus runs along the back and inner side of the thigh, from the lower pelvis to the upper-inner shin below the knee.

It begins at the ischial tuberosity, a bony prominence at the lower part of the pelvis. At its distal end, the tendon joins the sartorius and gracilis tendons at the pes anserinus, a shared insertion on the anteromedial proximal tibia. 

This location matters clinically because pain in the medial knee region can involve the pes anserinus complex, while pain high in the posterior thigh can involve the proximal hamstring tendons or surrounding structures.

What Does the Semitendinosus Do?

The semitendinosus has three main actions:

• Hip extension: Moves the thigh backward relative to the pelvis.
• Knee flexion: Bends the knee.
• Medial tibial rotation: Rotates the lower leg inward when the knee is flexed. Because it crosses both the hip and knee, the muscle manages changing tension at two joints during running and other athletic movements. It is heavily loaded during sprinting, particularly when the hamstring muscles contract eccentrically to control the moving leg. 

Semitendinosus vs. Semimembranosus

The semitendinosus and semimembranosus are both medial hamstrings. They arise from the ischial tuberosity and share the core functions of hip extension, knee flexion, and medial tibial rotation 

Feature	Semitendinosus	Semimembranosus
General tendon shape	Long, cord-like distal tendon	Broad, flatter distal tendon
Distal insertion	Pes anserinus on medial proximal tibia	Posteromedial proximal tibia with multiple expansions
Position	More superficial	Deeper and more medial
ACL graft use	Common hamstring autograft source	Not the usual harvested tendon
Clinical association	Can be involved in sprint-related strain; commonly harvested for ACL grafting	Can be involved in proximal hamstring and distal posteromedial knee disorders

The clinical patterns above are not absolute. Either medial hamstring can be involved in strains, tendinopathy, or other injuries, and accurate diagnosis requires clinical assessment rather than symptom location alone.

Semitendinosus and the Hamstring Group

All main hamstring muscles extend the hip and flex the knee. But they do not contribute equally in every movement. Their activation timing, lengthening velocity, architecture, and force demands differ during a running stride.

Hamstring strains are common in running and pivoting sports, with sprinting and rapid acceleration among the most frequent mechanisms. The biceps femoris is often reported as the most frequently injured hamstring in sprinting sports, but the semitendinosus and semimembranosus can also be affected in sprinting, kicking, stretching, and high-speed running injuries.

Why the Semitendinosus Matters in Running

The hamstrings work intensely during late swing in running, just before the foot contacts the ground. They lengthen while producing force to decelerate the swinging leg and control hip and knee movement.

This eccentric loading is an important contributor to sprint-related hamstring injuries. The exact injury mechanism varies with speed, fatigue, prior injury, tissue capacity, joint position, and the particular muscle or tendon involved. 

Semitendinosus Pain and Common Injuries

Semitendinosus-region symptoms can occur high in the posterior thigh, in the muscle belly, or near the medial knee. Pain location provides clues but cannot by itself determine the injured tissue.

Sprint-Type Injuries

Sprint-type hamstring injuries are commonly associated with high-speed running. Symptoms often include sudden posterior-thigh pain during acceleration or sprinting. Stretch-Type Injuries.s

Stretch-type injuries can occur when hip flexion combines with knee extension, such as during a high kick or forced stretch. These injuries can involve the proximal hamstring region but must be assessed individually.

Proximal Hamstring Tendinopathy

Deep pain near the ischial tuberosity (“sit bone”), particularly pain aggravated by prolonged sitting, can be consistent with proximal hamstring tendinopathy. The condition may involve one or more proximal hamstring tendons and should not automatically be attributed to the semitendinosus alone.

Distal Medial Knee Pain

Pain on the inner side just below the knee can involve the distal semitendinosus tendon, pes anserinus complex, or other medial knee structures. Persistent or worsening pain warrants assessment because several conditions can cause similar symptoms.

Semitendinosus Strain Symptoms

A semitendinosus or other hamstring strain can cause:

• Sudden, sharp pain during running, kicking, or stretching
• Posterior-thigh swelling or bruising
• Local tenderness
• Weakness or difficulty bending the knee
• Pain during stretch or resisted knee flexion
• Difficulty walking normally
• A visible or palpable defect in severe tears

Seek urgent clinical assessment if there is an audible pop, marked bruising, inability to bear weight, a large loss of strength, numbness, severe pain, or concern for a complete tear or tendon avulsion.

Diagnosis and Imaging

Diagnosis begins with the history and physical examination. Clinicians consider how symptoms began, the exact location of pain, bruising, range of motion, strength, ability to bear weight, and neurological findings.

Imaging is not needed for every uncomplicated hamstring strain. MRI can help when the diagnosis is uncertain, a substantial injury is suspected, the clinician needs to define the tissue involved, or the results may influence management. Ultrasound can also be useful in selected settings, particularly for superficial structures and serial assessment, but its value depends on operator skill and injury location.

Imaging should support—not replace—clinical assessment. MRI findings alone should not be treated as the sole criterion for return to sport 

Treatment and Recovery

Early management protects the injured area from high-strain loading while avoiding unnecessary prolonged rest. International hamstring-injury consensus guidance supports individualized, progressive rehabilitation based on symptoms, strength, response to loading, injury characteristics, and sport demands rather than a fixed calendar-based return timeline. Early Phase

In the first days after injury, priorities commonly include:

• Avoiding movements that sharply increase pain
• Using relative rest rather than complete immobility
• Compression and elevation when appropriate for swelling
• Seeking medical advice for significant injuries or medication questions
• Maintaining realistic expectations about recovery time

Rehabilitation Phase

As symptoms settle, rehabilitation typically progresses through:

• Gentle, pain-limited movement to maintain mobility
• Gradual strengthening, often beginning with isometric exercises
• Progressive hamstring loading through increasing ranges of motion
• Strengthening at longer muscle lengths when tolerated
• Running progression and sport-specific drills
• Criteria-based return to training and competition

Milder strains may improve within weeks, while significant muscle, tendon, or proximal injuries can take much longer. Previous hamstring injury is a known recurrence risk, which is why quality rehabilitation and graded return to high-speed running matter. 

Semitendinosus Exercises

Exercise selection depends on whether the goal is general strength, flexibility, injury prevention, or rehabilitation. After a suspected strain, surgery, or persistent pain, work with a physiotherapist or sports-medicine professional before beginning aggressive training.

General Strengthening

Romanian deadlifts, hamstring curls, bridge variations, and hip-hinge patterns can strengthen the hamstring group, including semitendinosus.

Flexibility

Use controlled, progressive flexibility work rather than forceful stretching, especially after a recent strain or with suspected proximal tendinopathy.

Strain Rehabilitation

A typical progression moves from pain-tolerated isometric loading to controlled dynamic exercise, longer-muscle-length loading, running drills, sprint exposure, and sport-specific tasks. The pace depends on symptoms, strength, movement quality, and tolerance to increasing load.

Injury Prevention

Eccentric hamstring training, including Nordic hamstring exercise variations, is commonly included in prevention programs for sports with repeated sprinting demands. Prevention should also consider running exposure, fatigue, prior injury, and the demands of the sport.

Proximal Hamstring Tendinopathy

Rehabilitation commonly begins by avoiding provocative compression while introducing tolerable loading. It then progresses toward heavier strengthening and sport-specific capacity over months rather than days or weeks. Individual assessment is important because other causes of deep buttock or posterior-thigh pain can mimic tendinopathy.

When to See a Doctor

See a doctor, physiotherapist, or qualified sports-medicine clinician promptly if:

• You heard or felt a pop at injury onset
• You cannot bear weight or walk normally
• Bruising or swelling is substantial
• There is visible deformity or a palpable gap
• Pain is severe or worsening
• Numbness, weakness, or unusual neurological symptoms occur
• Symptoms do not begin to improve after several days
• You have recurrent hamstring injuries
• You have persistent pain high near the sit bone or near the medial knee

Semitendinosus Tendon in ACL Reconstruction

The semitendinosus tendon is a common autograft source for ACL reconstruction. It is often harvested with the gracilis tendon, although surgeons may use a quadrupled semitendinosus tendon alone when appropriate graft size can be obtained. 

Graft selection is individualized. Outcomes depend on factors including activity level, age, anatomy, surgeon technique, associated injuries, rehabilitation, and the outcome being measured. Systematic evidence finds that quadriceps-tendon and hamstring-tendon autografts can both produce good ACL reconstruction outcomes, without one graft being universally best 

Some comparative evidence suggests semitendinosus-only grafting may preserve knee-flexor strength better during early recovery than combined semitendinosus-gracilis harvesting. Longer-term differences may narrow, and the practical importance for an individual patient varies.

A graft decision should be made with an orthopaedic surgeon using the patient’s sport, graft availability, occupation, knee history, rehabilitation plan, and personal priorities—not by one article’s ranking alone.

Tendon Regeneration After ACL Surgery

The semitendinosus tendon can regenerate after harvesting for ACL reconstruction, but regrowth varies considerably between patients.

A systematic review of 30 studies reported tissue regeneration at the harvest site in approximately 79% of semitendinosus tendons and 43% of gracilis tendons. The authors also noted that there is no universally accepted definition of tendon “regeneration,” and that imaging appearance, strength recovery, and clinical function do not always match perfectly

Regrowth can begin within months and may continue for years. The regenerated tissue may attach or blend with nearby structures around the pes anserinus. Some muscle retraction or strength deficits can persist, even when many daily activities and sports functions recover well.

This is an evolving research area. A 2026 prospective study reported incomplete hamstring strength recovery at two years in some patients and found that MRI evidence of regeneration at six months did not necessarily predict later strength recoveryy 

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