Author: Kevin B. Rosenbloom, C.Ped, Sports Biomechanist
Extension is another vital movement at the hip joint. This summary will briefly discuss hip extension, explore the muscle bodies that contribute to this movement and give samples into the research about the muscles.
Hip extension is the dorsal, superior raise of the thigh and leg at the hip joint. The mean range of motion for healthy male adults between 30-40 years of age has been placed as 9°; however, 30-35° is certainly obtainable (Roaas & Andersson 1982, Washington State DSHS 2014). Obviously greater ranges can be possible with flexible athletes: yoga instructors, gymnasts, etc. The piriformis, superior gemellus, inferior gemellus, biceps femoris long and biceps femoris short are all the most significant contributors to hip extension (Visible Body 2019). It is important to note that other sources have suggested more contribution from the posterior hamstring compartment and the gluteus maximus, and/or less contribution from the deep pelvic muscles.
Muscles of the Deep Buttock
The piriformis muscles are flat, triangular muscles with 3 heads that attach to grooves on both sides of the anterior sacrum within the pelvis. The bodies travel out of the pelvis via the greater sciatic foramen and into tendons that connect to the superior great femoral trochanter. The piriformis tendons often combine with the common tendons of both gemelli and obturator internus. The piriformis muscle is the topic of interesting debate regarding the distinction between under- and over-diagnosing piriformis syndrome, and its relation to sciatica (Michel et al. 2013, Cass 2015). It is agreed upon that the muscle can apply compression on the sciatic nerve, resulting in pain in the buttocks and lower back.
Both gemelli (superior and inferior) border and are accessories to the obturator internus tendon (Gray 1918). The superior gemelli are small and slender muscles that arise from both ischial spines and insert into the medial great femoral trochanter. The inferior gemelli begin at the ischial tuberosity, just inferior to the obturator internus, and insert to the medial great femoral trochanter, just superior to the trochanteric fossa.
Classifying these collection of muscles has been a topic of investigation. A previous study has suggested that although the superior and inferior gemelli, and obturator internus muscles are regarded as independent muscles in textbooks, under close examination they showed to be fused into one gemellus pocket (Shinohara 1995). It was also noted in Fernandes et al., that there was an absence of the superior gemellus altogether in their observations of an elderly cadaver (2013). However, classification of these muscles have determined that these muscles will be kept independent because of their nerve supply variations (Shinohara 1995, Aung et al. 2001).
Biceps Femoris: Posterior Compartment
Originating on the posterior portion of the ischial tuberosity, the biceps femoris muscles are part of the hamstring group and the long heads share common tendons with the semitendinosus and the semimembranosus muscles. As the long heads’ oblique fusiform body travels distally down the femur, the short heads origination begins beneath the long heads and from the lateral portions of the femoral linea aspera. Both heads insert into shared tendons on the lateral fibular head of both knees.
The biceps femoris is an interesting muscle. The short head is not necessarily always present and there can be variation in additional heads and insertion points (Gray 1918). Observations of the biomechanics of this muscle shows that while the hip is flexed or extended, it acts as a relatively weak knee flexor and hip extensor. Because both muscles insert into the lateral side just below the knees, finding their connecting tendons is relatively easy in an exam. Most general pain in the biceps femoris can have its cause traced to improper motion during weighted exercise or excessive exercise. These behaviors can often leading to tearing of the muscles and ligaments.
Muscle Overview - Hip Extensors
Figure 1. Sketch of Hip Flexors (Right), Posterior View.
Superior gemellus 
Inferior gemellus 
Biceps femoris long 
Biceps femoris short 
References & Works Cited
Aung, H. H., Sakamoto, H., Akita, K., Sato, T. 2001. “Anatomical Study of the Obturator Internus, Gemelli and Quadratus Femoris Muscles With Special Reference to Their Innervation,” The Anatomical Record 263;1: 41-52. https://doi.org/10.1002/ar.1075.
Barclay, T. 2018. “Anatomy Explorer,” innerbody.com. Accessed 19 Mar 2019. https://www.innerbody.com/anatomy/muscular/leg-foot.
Cass, S. P. 2015. “Piriformis Syndrome: A Cause of Nondiscogenic Sciatica,” Current Sports Medicine Reports 14;1: 41-44. https://journals.lww.com/acsm-csmr/fulltext/2015/01000/Piriformis_Syndrome___A_Cause_of_Nondiscogenic.12.aspx#pdf-link.
Fernandes, R. M. P., Lazzoli, J. K., Manaia, J. H. M., Babinski, M. A. 2013. “Bilateral Absence of Superior Gemellus Muscle in Elderly Cadaver,” International Journal of Morphology 31(3): 902-904. https://scielo.conicyt.cl/pdf/ijmorphol/v31n3/art20.pdf?origin%3Dpublication_detail.
Gray, H. 1918. “The Muscles and Fasciæ of the Lower Extremity,” Anatomy of the Human Body, 20th Ed. Lead & Febiger. Philadelphia & New York, USA. 420-1, 476, 478-9.
Michel, F., Decavel, P., Toussirot, E., Tatu, L., Aleton, E., Monnier, G., Garbuio, P., Parratte, B. 2013. “The piriformis muscle syndrome: An exploration of anatomical context, pathophysiological hypotheses and diagnostic criteria,” Annals of Physical and Rehabilitation Medicine 56; 300-311. https://doi.org/10.1016/j.rehab.2013.03.006.
Quinn, E. 2019. “Generally Accepted Values for Normal Range of Motion (ROM) in Joints,” verywellhealth.com. Accessed 19 Mar 2019. https://www.verywellhealth.com/what-is-normal-range-of-motion-in-a-joint-3120361.
Roaas, A., Andersson, G. B. J., 1982. “Normal Range of Motion of the Hip, Knee and Ankle Joints in Male Subjects, 30-40 Years of Age,” Acta Orthopaedica Scandinavica, 53:2, 205-208. https://www.tandfonline.com/doi/abs/10.3109/17453678208992202.
Visible Body. 2019. “Muscle Premium,” VisibleBody.com. Purchasable Application. Accessed 21 Feb 2019.Washington State DSHS. 2014. “Range of Joint Motion Evaluation Chart,” Washington State Department of Social & Health Services. Accessed 20 Mar 2019. https://www.dshs.wa.gov/sites/default/files/FSA/forms/pdf/13-585a.pdf.
Kevin B. Rosenbloom, C.Ped, Sports Biomechanist
Kevin B. Rosenbloom, founder and president of Kevin Orthopedic, is a renowned certified pedorthist and sports biomechanist practicing in Santa Monica, CA. With his continuing research on the historical development of foot and ankle pathologies, comparative evolution of lower extremities and the modern environmental impacts on ambulation, he provides advanced biomechanical solutions for his patients and clients.