what is semitendinosus?

Semitendinosus Muscle: Anatomy, Function, Clinical Relevance, and Rehabilitation

Introduction

The semitendinosus muscle is one of the three hamstring muscles located in the posterior compartment of the thigh. It plays a crucial role in lower limb movement, especially in knee flexion, hip extension, and dynamic stabilization of the pelvis during walking, running, and jumping. Its name “semitendinosus” refers to its long, cord-like tendon that extends distally, making it an important structure both anatomically and clinically.

The muscle is often involved in sports-related injuries, especially in athletes who require explosive sprinting or sudden directional changes. Understanding its anatomy, function, and clinical significance is essential for physiotherapists, sports medicine practitioners, and orthopedic specialists.

Anatomy of Semitendinosus Muscle

Origin

• Ischial tuberosity of the pelvis (shared origin with the long head of biceps femoris).

Insertion

• Medial surface of the proximal tibia, specifically at the pes anserinus (a conjoined tendon with gracilis and sartorius muscles).

Nerve Supply

• Tibial division of the sciatic nerve (L5, S1, S2).

Blood Supply

• Branches from the profunda femoris artery and inferior gluteal artery.

Structure

• The muscle has a long fusiform belly and a characteristic tendon that runs medially along the thigh before inserting into the tibia.

• It is located medial to the biceps femoris and superficial to the semimembranosus.

Function

• Primary Actions:

  • Knee flexion.

  • Hip extension.

• Secondary Actions:

  • Medial rotation of the tibia on the femur (when the knee is flexed).

  • Stabilization of the pelvis during walking and running.

Clinical Assessment

Palpation

1. Patient lies prone with knee flexed to 90°.

2. Ask patient to resist knee flexion.

3. Palpate the medial hamstring tendon just above the knee joint.

Muscle Power Testing

• Grade 0–5 scale using manual muscle testing (MMT).

• Resistance applied during knee flexion in prone position.

Length Assessment

• Performed via Straight Leg Raise (SLR) or Passive Knee Extension Test to assess hamstring flexibility.

Common Injuries & Clinical Relevance

• Hamstring Strain – Common in athletes; often occurs during eccentric contraction in sprinting.

• Tendinopathy – Overuse injury leading to pain and swelling at the pes anserinus.

• Tears – Partial or complete tears due to overstretching or forceful contraction.

• Pes Anserinus Bursitis – Inflammation near insertion causing medial knee pain.

Therapeutic Exercises

Strengthening Exercises

1. Prone Leg Curls

   • Patient lies prone and flexes the knee against resistance.

2. Romanian Deadlifts

   • Strengthens hamstrings eccentrically.

3. Nordic Hamstring Curl

   • Effective for injury prevention and rehabilitation.

Stretching Exercises

1. Seated Hamstring Stretch

   • Sit with legs extended, lean forward keeping the back straight.

2. Supine Hamstring Stretch with Strap

   • Use a strap around the foot to pull the leg upward for a controlled stretch.

Trigger Points

• Typically located in the muscle belly.

• Can cause referred pain along the posterior thigh and behind the knee.

Rehabilitation & Prevention

• Progressive eccentric loading (Nordic curls).

• Flexibility programs focusing on hamstring and hip mobility.

• Sports-specific drills for athletes.

• Adequate warm-up and cool-down routines.

FAQs

1. Where is the semitendinosus muscle located?
It is located in the back of the thigh, medial to the biceps femoris and superficial to the semimembranosus.

2. What is the main function of the semitendinosus muscle?
Its primary functions are knee flexion and hip extension, with a role in medial rotation of the tibia.

3. How is the semitendinosus muscle injured?
It is commonly injured during sports that involve sprinting, sudden acceleration, or rapid directional changes.

4. How can I strengthen my semitendinosus muscle?
Exercises like Nordic hamstring curls, Romanian deadlifts, and prone leg curls are effective for strengthening.

5. What is the pes anserinus?
It is a combined tendon formed by the gracilis, sartorius, and semitendinosus muscles inserting on the medial tibia.

6. What is the difference between semitendinosus and semimembranosus?
A: Both are medial hamstrings, but semitendinosus has a long tendon and inserts at the pes anserinus, while semimembranosus has a broader insertion at the medial tibial condyle.

7. How can I tell if I have injured my semitendinosus muscle?
A: Sharp posterior thigh pain during running or bending the knee, swelling, and tenderness over the medial hamstring area are common signs.

 8. Can semitendinosus muscle injuries heal without surgery?
A: Most strains and partial tears heal with conservative physiotherapy and rest, but severe avulsions may need surgery.

9. Which sports put the semitendinosus muscle at the highest risk?
A: Sprinting, football, basketball, and gymnastics due to rapid acceleration and deceleration forces.

References

1. Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Elsevier; 2020.

2. Brukner P, Khan K. Brukner & Khan's Clinical Sports Medicine. 5th ed. McGraw-Hill; 2017.

3. Orchard JW, Best TM, Verrall GM. Return to play following muscle strains. Clin J Sport Med. 2005;15(6):436–441.

4. Kendall FP, McCreary EK, Provance PG. Muscles: Testing and Function with Posture and Pain. 5th ed. Lippincott Williams & Wilkins; 2005.

5. Opar DA, Williams MD, Shield AJ. Hamstring strain injuries: factors that lead to injury and re-injury. Sports Med. 2012;42(3):209–226.