Human Movement Science & Functional Anatomy of the:

Semitendinosus and Semimembranosus

by Brent Brookbush MS, PES, CES, CSCS, ACSM H/FS

By Any Other Name:

• These muscles are often referred to as the "medial hamstrings", in opposition to the "lateral hamstrings (a.k.a.the biceps femoris)". They are often abbreviated the "Semi's".

Note: the semitendinosus and semimembranosus, the continuation into the sacrotuberous ligament, and the innervation via the tibial branch of the sciatic nerve.

Semitendinosus:

• Origin: Tuberosity of ischium by tendon common with with the long head of the biceps femoris (11).
• Insertion: Proximal part of the medial surface of the tibia and deep crural fascia. The tendon of the semitendinosus contributes the distal fibers of the pes anserinus tendon - a tendon that is comprised of the distal tendons of the semitendinosus, gracilis and sartorius (11,16).
  • The semitendinosus is a superficial muscle of the posterior thigh, bordered by the long head of the biceps femoris laterally, and the semimembranosus medially (along with portions of the adductor magnus). All of the hamstring muscles (including the biceps femoris ) lay in the posterior compartment of the thigh, with the semitendinosus bordered anteromedially by the posteromedial intermuscular septum.
    • * The semitendinosus can be palpated with relative ease by locating the space between the two large bands that comprise the hamstring tendons just superior to the posterior knee. As you course your fingers up the "valley" created by the division in the hamstrings. You can feel musculotendinous junction invest into the long cylindrical muscle bellies. The muscle just medial to this valley is the semitendinosus. With a little exploration the division between the semitendinosus and semimembranosus can be be felt.
• Nerve: Tibial nerve; a branch of the sciatic nerve via the sacral plexus, originating from nerve roots L5 - S2 and sometimes L4 (3).
• Action:
  • Hip: Extension and a weak medial rotator
  • Knee: Flexion and tibial internal rotation

If you follow the sacrotuberous ligament to the right on this cadaver photo you can see how this ligament courses into the common tendon of the biceps femoris (underneath the sciatic nerve) and semitendinosus (right below it). - www.rvuanatomy.com

Semimembranosus

• Origin: Tuberosity of ischium, proximal and lateral to the common tendon of the biceps femoris and semitendinosus (11).
• Insertion: Posteromedial aspect of the medial condyle of the tibia, with expansions into the posterior oblique ligament, poplitial ligament, popliteus fascia, posterior joint capsule.
  • The semimembranosus is also superficial muscle of the posterior thigh, bordered by the long head the semitendinosus laterally and adductors medially. Much of the semimembranosus lies deep to the semitendinosus. All of the hamstring muscles (including the biceps femoris ) lay in the posterior compartment of the thigh; the semimembranosus is bordered anteriorly by the posteromedial intermuscular septum.
    • The semitendinosus can be palpated with relative ease by locating the space between the two large bands that comprise the hamstring tendons just superior to the posterior knee. As you course your fingers up the "valley" created by the division in the hamstrings. You can feel musculotendinous junction invest into the long cylindrical muscle bellies. The muscle just medial to this valley is the semitendinosus, the muscle just medial and deep to that (in essence the medial aspect of the medial hamstrings) is the semimembranosus. With a little exploration the division between the semitendinosus and semimembranosus can be be felt.
• Nerve: Tibial nerve; a branch of the sciatic nerve via the sacral plexus, originating from nerve roots L5 - S1 and sometimes L4 and/or S2 (3).

Action:

• Hip: Extension and a weak medial rotation
• Knee: Flexion and tibial internal rotation

Note the insertion of the semimembranosus tendon into the complex posterior oblique ligament, the popliteal ligament, and investment of these structures into the distal MCL - http://ajs.sagepub.com/content/32/2/337/F4.large.jpg

Cadaver dissection of posteromedial corner of the knee - http://www.hindawi.com/journals/ari/2012/151342/fig1/

Integrated Function:

• Stabilization:
  • The semimembranosus aids in hip and knee stabilization, specifically the posterior medial compartment where it reinforces the capsule and increases tension on the posterior oblique ligament, popliteal ligaments, popliteal fascia and posterior capsule.
  • The semitendinosus stabilizes the medial knee, hip and may stabilize the sacroiliac joint via the sacrotuberous ligament and common tendon with the biceps femoris.
• Eccentrically Decelerates:
  • The semitendinosus and semimembranosus eccentrically decelerate hip flexion, external rotation and abduction, as well as, knee extension and tibial external rotation.
• Synergists:
  • The semimembranosus and semitendinosus are synergists of hip extension along with the biceps femoris , adductor magnus , and the prime mover of hip extension, the gluteus maximus .
  • Both the semimembranosus and semitendinosus aid in knee internal rotation, along with the gracilis , popliteus, and medial gastrocnemius.
  • The semitendinosus aids the biceps femoris in sacral extension via a common tendon that runs continuous with the sacrotuberous ligament.
  • The semitendinosus may have a stronger synergistic relationship with the gracilis , and sartorius via the pes anserinus tendon.
  • The semimembranosus may have a stronger synergistic relationship with the popliteus via fascial continuity to the popliteal fascia.

Cross-section of the leg - By Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below)Bartleby.com: Gray's Anatomy, Plate 432, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3450591

Subsystems

• The semimembranosus and semitendinosus play no specific role in the core subsystems , although more research should be done to determine if the common tendon shared by the semitendinosus and biceps femoris implicates the semitendinosus in Deep Longitudinal Subsystem (DLS) involvement.

Note the common tendon shared by the semitendinosus and biceps femoris proximally, and the fascial continuity with the sacrotuberous ligament

Arthrokinematics:

• The semitendinosus and semimembranosus contributes to superior glide and posterior rotation of the femoral head in the acetabulum. Due to the relatively distal attachment it is difficult to determine whether or not these muscles contribute to anterior or posterior glide (3). The semitendinosus, as mentioned above, will contribute to stabilization, counter-nutation and extension of the sacroiliac joint via the common proximal tendon with the biceps femoris and fascial continuity with the sacrotuberous ligament (16).
• The arthrokinematic function of these muscles at the knee is a bit more complex. Although both muscles will contribute to posterior glide and tibial internal rotation, their attachments to the anteromedial (semitendinosus) and posteromedial (semimembranosus) aspects of the knee may imply separate roles in stabilization, glide, and roll that are distinct from one another. For example, the semitendinosus invests in the pes anserinus tendon with fascial slips to the medial collateral ligament (MCL), implying a function in lateral stabilization and resisting lateral glide of the tibia. The semimembranosus invests in the posterior oblique tendon, poplitial tendon, popliteal fascia, and posterior capsule implying a larger role in stabilization of the posterior knee, hyper extension, and resisting anterior glide in extension (although the semitendinosus can also play a role in resisting anterior glide via attachment to the anterior tibia).

Great picture of the knee and investing tendons, ligaments, and fascia. -www.wikipedia.com

Fascial Integration:

• * * My Fascial Hypothesis: Large fascial sheaths not only play a role in the transmission of mechanical force, but may also play a role in dictating the function of muscular synergies. This is likely caused by reducing or increasing tone of invested musculature via reflex arcs formed between mechanoreceptors embedded in the connective tissue and the attached musculature. In this way my view of fascia differs slightly from noted expert on the subject Tom Myers. I think of these large fascial sheaths (specifically the thoracolumbar fascia, iliotibial band, and abdominal fascial sheath) as natures "mother board." A place for mechanical information to be communicated to the nervous system for more efficient recruitment of the muscular system. Despite having a slightly different philosophy it does not change the fact that fascia plays an important communicative role in the human body and we have Tom Myers to thank for his work.

Fascial Integration of the Semimembranosus and Semitendinosus:

• * * * The semimembranosus and semitendinosus have complex fascial relationships that are worthy of further research.

* * The semitendinosus shares a common tendon with the [biceps femoris](https://brentbrookbush.com/online-courses/articles/muscular-anatomy/biceps-femoris/ "Biceps Femoris").  This may imply that these muscles share roles in stabilizing the sacroiliac joint via the sacrotuberous ligament, but also may imply that these muscle behave similarly relative to sacral motion in regard to changes in length and activity (tonicity).  This could implicate the semitendinosus as a muscle of the [Deep Longitudinal Subsystem (DLS)](https://brentbrookbush.com/online-courses/articles/core-subsystems/deep-longitudinal-subsystem/ "Deep Longitudinal Subsystem (DLS)").  The quandary of this implication is the fact the the biceps femoris and semitendinosus are antagonist relative to rotation of the tibia at the knee. * The semitendinosus shares a tendinous structure with the [gracilis](https://brentbrookbush.com/online-courses/articles/muscular-anatomy/adductors/ "Adductors") and [sartorius](https://brentbrookbush.com/articles/muscular-anatomy/sartorius/).  The idea that the pes anserinus group contributes to medial stabilization and internal rotation of the tibia is nothing new, but are there relationships between the pes anserinus group and the medial patellar retinaculum and potentially activity of the [tibialis anterior](https://brentbrookbush.com/online-courses/articles/muscular-anatomy/tibialis-anterior/ "Tibialis Anterior") via the investment in deep crural fascia?  Further, does the differentiation between distal attachments of the "semi's" pay a role in recruitment patterns during knee motion?

* The semimembranosus, via investment in the posterior capsule, posterior oblique ligament, popliteal ligament, and popliteal fascia may imply that activity of the semimembranosus and popliteus are linked.  Further, the recruitment of these muscles may be equally affected by changes in length and force imparted on the posteromedial knee (example, eccentric deceleration of knee extension and internal rotation). This relationship is distinct from the semitendinosus, once again implying separate activity between these two muscles.

* Although I could not find a specific image, cadaver dissection, study or text, I would be curious to find out if any relationships exists between the semimembranosus and adductor magnus via there proximal attachments.

* Last, Tom Myer's mentions that the lateral and medial hamstrings becoming bound together in his book "Anatomy Trains" (6).  This would result in an inability of the medial and lateral hamstrings to impart separate forces during motion, disrupting the delicate balance between supination/pronation, tibial internal/external rotation, and femoral internal/external rotation.  If combined with common movement impairment, including over-activity of the [biceps femoris](https://brentbrookbush.com/online-courses/articles/muscular-anatomy/biceps-femoris/ "Biceps Femoris"), this could result in arthrokinematic dyskinesis at the knee.

Muscles inserting into the Pes Anserinus Tendon (including the Semitendinosus) – http://2.bp.blogspot.com/online-courses/online-courses/_j_szTjYOyds/SPjLBAlHQlI/AAAAAAAADyE/VXnNt5lg-jo/s320/knee_bursitis_pes_anserine_anatomy01.jpg

Behavior in Postural Dysfunction:

These muscle are prone to adaptive lengthening and under-activity. When addressed, these muscle should be activated; stretching these muscles is not recommended. Release of the semitendinosus may be acceptable in the presence of SIJD.

• In Upper Body Dysfunction (UBD) these muscles do not play a significant role, unless over-activity and adaptive shortening of the latissimus dorsi is related to Sacroiliac Joint Dysfunction (SIJD ). Even then, this muscle would not be a priority in programming.
• In Lower Leg Dysfunction (LLD)  these muscles play their most significant role. The inability of the semitendinosus and semimembranosus to eccentrically decelerate tibial external rotation results in "feet turn out" and dyskinesis of the hip, knee and ankle. Generally this is paired with over-activity of the tibial external rotators and/or the Deep Longitudinal Subsystem (DLS) .
• In Lumbo Pelvic Hip Complex Dysfunction (LPHCD) the semitendinosus, semimembranosus, and the long head of the biceps femoris are long. STRETCHING IS NOT RECOMMENDED. Activation of the semi's is recommended. In Sacroiliac Joint Dysfunction (SIJD)  it may be appropriate to activate only on the side opposite dysfunction.

In short, these muscles should be the focus of activation exercise when postural dysfunction is noted (signs of length change listed below). More techniques are desperately needed. Commonly, leg curls with hip and knee internal rotation are given as part of an exercise program, but in my own practice I have found this to increase adductor activity  resulting in a loss of hip abduction range of motion.

May Contribute to the Following Impairments:

• Knee Pain
  • Patellar tendonitis (Jumper's Knee)
  • Lateral knee pain (Runner's Knee)
  • Iliotibial band syndrome
  • Hamstring tendonitis
  • Generalized knee pain
• Hamstring Strain
  • Proximal hamstring avulsion
• Sacroiliac Joint Pain and Dysfunction
• Hip Pain
  • Impingement Syndrome
  • Ischial tuberosity bursitis
  • Generalized hip pain
• Lumbar spine pain
  • Excessive lordosis
• Lateral shift of lumbar spine
• Ankle/Foot Pain
  • Ankle sprain
  • Ankle impingement
  • Achilles tendonitis
  • Plantar fasciitis

Signs of Altered Length/Tension and Tone:

• Overhead Squat:
  • Feet Turn Out: Long/Under-active
  • Knees Bow In: Long/Under-active
  • Anterior Pelvic Tilt: Long/Under-active
  • Excessive Forward Lean: Long/Under-active
  • Asymmetrical Weight Shift: Long/Under-active side opposite dysfunction
• Goniometric Assessment
  • Excessive External Rotation at Hips: > 45°

Palpation of the Semimembranosus and Semitendinosus:

• Although release techniques are generally not recommended for long/under-active muscles, occasionally long muscles develop active trigger points. Be judicious in your use of release techniques for this musculature.

Hamstring Trigger Points for the Semi's and Biceps Femoris - www.triggerpoints.net

Video Snippets of Live Workshops:

• Postural Dysfunction involving the Semitendinosus and Semimembranosus

"Knees Bow In" Break Down:

"Feet Turn Out" Break Down:

"Anterior Pelvic Tilt" Break Down:

Exercises involving the Semitendinosus and Semimembranosus:

Tibial Internal Rotator Activation:

Bibliography:

• * 3. Phillip Page, Clare Frank , Robert Lardner , Assessment and Treatment of Muscle Imbalance: The Janda Approach © 2010 Benchmark Physical Therapy, Inc., Clare C. Frank, and Robert Lardner

6. Dr. Mike Clark & Scott Lucette, “_NASM Essentials of Corrective Exercise Training_” © 2011 Lippincott Williams & Wilkins

9. Donald A. Neumann, “Kinesiology of the Musculoskeletal System: Foundations of Rehabilitation – 2nd Edition” © 2012 Mosby, Inc.

12. Michael A. Clark, Scott C. Lucett, _NASM Essentials of Personal Training: 4th Edition_, © 2011 Lippincott Williams and Wilkins

15. Leon Chaitow, _Muscle Energy Techniques: Third Edition_, © Elsevier 2007

18. Tom Myers, _Anatomy Trains: Second Edition_. © Elsevier Limited 2009

21. Shirley A Sahrmann, _Diagnoses and Treatment of Movement Impairment Syndromes,_ © 2002 Mosby Inc.

24. David G. Simons, Janet Travell, Lois S. Simons, _Travell & Simmons’ Myofascial Pain and Dysfunction, The Trigger Point Manual, Volume 1. Upper Half of Body: Second Edition_,© 1999 Williams and Wilkens

27. Cynthia C. Norkin, D. Joyce White, Measurement of Joint Motion: A Guide to Goniometry – Third Edition. © 2003 by F.A. Davis Company

30. Cynthia C. Norkin, Pamela K. Levangie, _Joint Structure and Function: A Comprehensive Analysis: Fifth Edition_ © 2011 F.A. Davis Company

33. Florence Peterson Kendall, Elizabeth Kendall McCreary, Patricia Geise Provance, Mary McIntyre Rodgers, William Anthony Romani__,_ Muscles: Testing and Function with Posture and Pain: Fifth Edition © 2005 Lippincott Williams & Wilkins_

36. Andrew Biel, Trail Guide to the Human Body: 4th Edition, © 2010

39. Carolyn Richardson, Paul Hodges, Julie Hides.  Therapeutic Exercise for Lumbo Pelvic Stabilization - A Motor Control Approach for the Treatment and Prevention of Low Back Pain: 2nd Edition (c) Elsevier Limited, 2004

42. Craig Liebenson, Rehabilitation of the Spine: A Practitioner's Manual, (c) 2007 Lippincott Williams & Wilkins

45. Stuart McGill, Low Back Disorders: Second Ediction © 2007 Stuart M. McGill

48. Robert Schleip, Thomas W. Findley, Leon Chaitow and Peter A. Huijing.  Fascia: The Tensiona Network of the Human Body.  (c) 2012 Elsevier Ltd.

© 2013 Brent Brookbush

Questions, comments, and criticisms are welcome and encouraged.