Semimembranosus Trigger Points

Introduction

The semimembranosus is a deep hamstring muscle responsible for knee flexion, hip extension, and posterior thigh stability. When trigger points develop in this muscle, they can cause posterior thigh pain, knee stiffness, and tightness in the lower leg, often mimicking hamstring strain, sciatic nerve irritation, or knee joint dysfunction.

Name and Area

  • Name: Semimembranosus

  • Area: Located in the posterior thigh, running from the ischial tuberosity (sit bone) to the medial tibia.

Indications

Semimembranosus trigger points may contribute to:

  • Pain in the back of the thigh and knee (mistaken for hamstring strain or sciatic pain)

  • Pain or tightness that extends to the inner knee and calf (can mimic nerve compression or medial knee dysfunction)

  • Stiffness in the hamstrings that restricts knee flexion and hip extension

  • Pain when walking, running, or sitting for long periods (common in athletes, runners, and office workers)

  • Weakness in knee flexion (difficulty bending the knee while running or climbing stairs)

  • Pain that worsens with sprinting, jumping, or sudden acceleration movements

Pain from this muscle is often mistaken for hamstring injuries, knee dysfunction, or sciatic nerve compression.

Muscle Action

  • Flexes the Knee: Bends the leg backward, essential for walking, running, and jumping.

  • Extends the Hip: Helps move the thigh backward, important for gait mechanics and sprinting.

  • Medially Rotates the Lower Leg: Assists in stabilizing the knee joint during movement.

The semimembranosus is crucial for lower body power, knee stability, and hip mobility.

Signs and Symptoms

Individuals with semimembranosus trigger points often report:

  • Pain along the back of the thigh that feels like a deep, aching sensation

  • Pain or tightness that extends into the inner knee or upper calf

  • Restricted hamstring flexibility, making it difficult to fully extend the leg

  • Pain that increases with sprinting, deep squats, or explosive leg movements

  • Difficulty bending the knee without discomfort or weakness

  • Pain that worsens after long periods of sitting or standing

Pain worsens with excessive knee flexion, prolonged sitting, or sudden sprinting movements.

Perpetuating Factors

Common causes of semimembranosus trigger points include:

  • Overuse in running, sprinting, or jumping sports (common in soccer, basketball, track and field, and gymnastics)

  • Prolonged sitting with knees bent (can lead to chronic tightness and restricted mobility)

  • Weak or imbalanced gluteal and quadriceps muscles (forces the hamstrings to compensate for stability)

  • Poor sprinting mechanics or sudden acceleration (can cause microtears and trigger point formation)

  • Insufficient hamstring stretching or recovery after intense exercise

Trigger Point Referral Pattern

Trigger points in the semimembranosus refer pain to:

  • The posterior thigh and knee (Can Mimic Hamstring Strain or Sciatic Pain)

  • The medial knee and upper calf (Mistaken for Knee Joint Dysfunction or Nerve Irritation)

  • The inner thigh and groin (Can Resemble Adductor Strain or Hip Dysfunction)

Pain from this muscle is often confused with hamstring tendinopathy, sciatic nerve irritation, or knee instability.

Differential Diagnosis

Semimembranosus trigger points may be mistaken for:

  • Hamstring strain (pain in the posterior thigh, common in runners and athletes with sudden leg movements)

  • Sciatica (pain radiating down the back of the leg, often due to nerve compression in the lower back)

  • Knee ligament injury (pain in the inner knee, can mimic MCL strains or meniscus tears)

  • Pes anserinus bursitis (pain on the medial side of the knee, worsens with running or stair climbing)

  • Gluteal dysfunction (weakness or imbalances in the hips that affect leg mechanics and knee stability)

A thorough hip, knee, and lower limb examination is necessary to rule out these conditions.

Associated Trigger Points

Semimembranosus trigger points often co-exist with:

  • Biceps femoris (lateral hamstring and knee pain, affects sprinting and jumping mechanics)

  • Adductor magnus (inner thigh and groin pain, can contribute to hip and pelvic imbalances)

  • Gluteus maximus (buttock and posterior thigh pain, affects hip extension and lower limb power)

  • Quadratus femoris (deep hip pain, affects external rotation and hip stability)

Anatomy and Innervation

Muscle Origin Insertion Innervation
Semimembranosus Ischial tuberosity (sit bone) Medial tibia (pes anserinus area) Tibial branch of the sciatic nerve (L5–S2)

The semimembranosus is innervated by the tibial branch of the sciatic nerve, which also controls knee flexion, hip movement, and lower limb coordination.

Patient Examination

A comprehensive examination should include:

  • Palpation: Identify tender nodules along the posterior thigh and medial knee.

  • Resisted Knee Flexion Testing: Assess pain and weakness when bending the knee against resistance.

  • Gait and Postural Analysis: Look for hip instability, excessive knee valgus, or altered stride mechanics.

  • Hamstring Flexibility and Strength Testing: Rule out muscle imbalances, tightness, or previous hamstring injuries.

Corrective Actions

Dry Needling

  • Dry needling can release trigger points in the semimembranosus, reducing thigh tightness and improving knee function.

Manual Therapy

  • Trigger Point Release: Apply deep sustained pressure to tight spots in the posterior thigh and medial knee.

  • Massage Therapy: Helps improve circulation and reduce hamstring muscle tension.

Stretching

  • Seated Hamstring Stretch: Helps lengthen the semimembranosus and improve flexibility.

  • Lunge Stretch With Knee Extension: Helps reduce tension in the posterior thigh and knee.

Strengthening Exercises

  • Nordic Hamstring Curls: Strengthens the hamstrings for better knee stability and injury prevention.

  • Single-Leg Romanian Deadlifts: Improves posterior chain activation and hip stability.

  • Glute Bridges: Helps counteract hamstring tightness and engage the posterior chain.

Postural and Movement Adjustments

  • Avoid overloading the hamstrings without proper warm-up (ensure dynamic stretching before running or sprinting).

  • Improve running mechanics (engage the core and avoid overstriding to reduce hamstring overuse).

  • Incorporate dynamic hip mobility drills (prevents excessive tightness and improves functional movement).

Conclusion

The semimembranosus plays a crucial role in knee flexion, hip stability, and lower body power, but trigger points in this muscle can cause significant posterior thigh, knee, and calf pain. By incorporating dry needling, manual therapy, stretching, and strengthening exercises, individuals can reduce pain, improve mobility, and prevent chronic hamstring dysfunction.

➡️ Learn more about Trigger Points

➡️ Explore our Trigger Point Index

Sources:

  • Travell, J. G., & Simons, D. G. (1983). Myofascial Pain and Dysfunction: The Trigger Point Manual (2nd ed.). Williams & Wilkins.

  • Simons, D., & Travell, J. (1999). The Trigger Point Manual, Volume 2: The Lower Extremities. Williams & Wilkins.