Secondary Logo

Journal Logo

Special Communications

Iliopsoas the Hidden Muscle: Anatomy, Diagnosis, and Treatment

Lifshitz, Liran BPt, MSc, PT; Bar Sela, Shlomo BPt MPE; Gal, Noga BPt, MSc; Martin, RobRoy PhD, PT; Fleitman Klar, Michal BPt

Author Information
Current Sports Medicine Reports: June 2020 - Volume 19 - Issue 6 - p 235-243
doi: 10.1249/JSR.0000000000000723

Abstract

Introduction

The term iliopsoas syndrome is a nonspecific term used to describe iliopsoas tendinopathy, iliopectinal bursitis, and/or internal snapping (1). The iliopsoas is important clinically, since impairments associated with this muscle group can be involved in orthopedic conditions of the spine, hip, and knee. Extraarticular anterior hip and groin pain are commonly associated with iliopsoas pathology but also may result from other structures that surround the hip.

Little has been written on iliopsoas pathology and the interventions directed at associated impairments and function limitations. The aim of this article is to expand the knowledge regarding this muscle group based on clinical experience and the existing literature.

Iliopsoas Anatomy

The psoas major is a long muscle, originating from the transverse processes, vertebral bodies, and intervertebral disks of T5 to L5. The iliacus is a shorter muscle, originating from the superior two thirds of the iliac fossa, ventral lip of the iliac crest, and sacral ala. There are medial and lateral bundles associated with the iliacus (2,3). The psoas major and iliacus converge to form the iliopsoas muscle at the L5 to S2 levels and inserts on the lesser trochanter of the femur as the iliopsoas tendon (2,3). The iliopsoas tendon has some variants with single, double, or triple tendon bundles. The psoas major tendon is located medial to the more lateral iliacus tendon (4). The deep portion of the iliopsoas muscle is located anterior and lateral to the labrum of the hip joint. This close relationship between the iliopsoas and labrum may have clinical relevance and can be associated with intraarticular hip impairment and pathology. The iliopectineal or iliopsoas bursa is the largest bursa in the human body located between the iliopsoas muscle, bony surface of the pelvis, and proximal femur (2,3).

The psoas minor is separate from the psoas major and iliacus muscles. It is located in the posterior wall of the abdomen, lateral to the lumbar spine (5), and present in only 59% to 65% of individuals (3,5,6). When present, it originates on the T12 and L1 vertebrae to attach on the iliopubic eminence and, therefore, functions as a weak trunk flexor with no action on the lower extremity.

The femoral triangle is located in the anterior hip and bordered by the inguinal ligament anteriorly, sartorius laterally, and the adductor longus medially. The floor of the triangle contains the iliopsoas and pectineus muscles, as well as blood vessels and nerves. Therefore, the triangle is a place to identify muscular trigger points in the iliopsoas (Fig. 1).

Figure 1
Figure 1:
Iliopsoas anatomy. © F. Netter, MD.

Function

The iliopsoas is the primary hip flexor and may assist in tilting the pelvis anteriorly. It also functions as an external rotator of the hip (7) and is considered to be a core muscle because of its attachments to the spine (8). Because the iliopsoas muscle connects the spine and lower extremity, it plays an important role in many activities of daily living, including sports. For instance, the psoas major assists in sitting and maintaining in an erect position of the spine (3,9). The iliopsoas contributes significantly to running, especially initiating the swing phase, as it performs early and rapid hip flexion (3,10,11). High activation of the iliopsoas also has been observed in a kicking motion (12). It has been shown that the iliopsoas muscle is active throughout the entire kicking movement, including during deceleration of the thigh (13).

Iliopsoas Clinical Relevance

The iliopsoas is often overlooked in the diagnostic process in those with lumbar spine and lower extremity injuries. However, due to its anatomy and function, impairments of the iliopsoas should be considered in those with low back and lower extremity pathology.

Acute groin injuries

The iliopsoas is frequently involved in acute groin injuries as 17% to 25% of all acute groin injuries are iliopsoas related (14). This type of injury often occurs in sports, especially those that involve kicking and/or changing directions (14).

Low back pain

The interrelationship between the hip and spine is supported in the literature, as a loss of hip motion was found to contribute to lumbar spine pain and disability (15–21). Specifically, hip disorders that cause a limitation in terminal hip extension can aggravate and/or cause lumbopelvic pain secondary to increased pelvic rotation, hyperlordosis, and facet overload (22–24). In addition, the psoas major activation is associated with compressive and shear forces on the spine (25) while acting as a lumbar spine stabilizer (9). Moreover, the study by Avrahami and Potvin (26) found stretching the iliopsoas muscle, decreased pain and disability with patients with low back pain. This is consistent with the authors' clinical experience, as identifying and treating a loss of hip extension from iliopsoas inflexibility has resulted in successful outcomes in patients with low back pain.

Pelvic pain

The iliopsoas acts as a pelvic and hip stabilizer, especially during single leg stance activities (3,27). This is particularly true of the iliacus muscle with its origin being on the pelvis. In addition, the iliopsoas also functions to tilt the pelvis anteriorly. Therefore, the iliopsoas may be important in those undergoing pelvic rehabilitation.

Overuse injuries

Iliopsoas injury is the second most common groin injury in soccer (28). With iliopsoas overuse injuries, ultrasound or magnetic resonance imaging scans commonly identify tendinopathies, tendinosis, or thickening of the tendon. Although commonly overlooked, muscle spasms and trigger points also are related to overuse injuries in the iliopsoas muscle.

Postoperative pain

During the first few days after hip surgery, patients often complain of significant pain as they maintain their hip in a flexed position for comfort and to protect their incision. In this flexed position, the iliopsoas muscle is highly active and, therefore, prone to muscle spasm. From the authors' experience, anterior hip pain after surgery is commonly related to the iliopsoas.

Hip snapping

There are different reasons for hip snapping. Iliopsoas or internal hip snapping is described as a painful audible and/or palpable snapping of the iliopsoas over the iliopectineal eminence. This snapping can occur as the hip is brought from a position of flexion, abduction, and external rotation (FABER) to extension (3). It should be noted that this snapping is not always symptomatic (3). Iliopsoas snapping also may be associated with deeper structures, such as the head of the femur and/or iliopectineal line.

Other

As noted above, the hip labrum and iliopsoas are in close proximity. Because the psoas tendon crosses the anterior part of the hip joint, it might have a role in symptomatic acetabular labral impingement (29). This anatomical relationship may be of particular importance in those with labral pathology and a tight iliopsoas tendon (29).

Moreover, because the iliopsoas muscle group is in close anatomical proximity to the abdominal area, there is a connection between the iliopsoas and the diaphragm, respiratory system, and other internal systems. However, there is a gap of knowledge regarding these connections.

Examination

Examination of the iliopsoas muscle group can be divided into three parts: medical history, clinical examination, and imaging. While imaging may provide useful information, it is outside the scope of this article.

The medical history (subjective examination)

The medical history of those with pathology and impairments associated with the iliopsoas muscle group can be challenging because there may not be unique symptoms that are different from other common hip problems. Therefore, medical history alone is often not enough for detecting an iliopsoas-related problem. Because the common complaint of those with iliopsoas pathology is anterior hip and/or groin pain, it is commonly confused with intraarticular hip pathology, such as femoroacetabular impingement syndrome (FAIS). Those with iliopsoas-related pain often have more superficial diffuse anterior hip pain, as opposed to the deep, well localized groin pain associated with intraarticular hip pathology. Pain while kicking (especially during the back-swing), walking with large steps, uphill running, and climbing stairs are common complaints in those with iliopsoas pathology. In some cases, low back pain also may be reported.

The clinical examination (objective examination)

A structured clinical examination provides important information related to differential diagnosis. For those with potential iliopsoas pathology, five tests are recommended and include an assessment of muscle function, flexibility, and palpation.

The first three tests are commonly used to assess for potential iliopsoas muscle involvement:

  1. An isometric-resistance muscle test: this test is used to evaluate muscle strength and pain reproduction. Clinically, when hip flexor muscle strength is decreased with reproduction of pain, the iliopsoas muscle is typically involved. From the authors' experience, we have found that the ideal position to test the iliopsoas muscle is supine with the hip and knee flexed to 90 degrees.
  2. Modified Thomas Test: This commonly performed test is used to evaluate the flexibility of the hip flexors. The main difference between the Thomas test and the modified Thomas test is that in the Thomas test, the patient is lying flat on the examination table, while in the modified test, the patient is lying on the edge of the table (Fig. 2). Although commonly used, studies reporting on the validity and reliability of the test are limited (30). To properly interpret test results, it is important to remove the lumbar lordosis. The tested limb should be lowered off the table edge with the hip angle being evaluated relative to the horizontal axis (30) as the clinician assess for reproduction of pain and tightness. The authors have found that when the iliopsoas is involved, pain can be reproduced during this test.
  3. Palpation: With palpation it is important to map out painful areas and connect them to the relevant anatomical structures. There are three main palpation points to assess in those with potential iliopsoas pathology: the first palpation point is just medially to the anterior superior iliac spine (ASIS) where the iliacus muscle can be assed. The second point is just medial (1 cm to 2 cm) to that, at which point the therapist can palpate the psoas major muscle. The third point of palpation is just below the inguinal ligament where the iliopsoas muscle can be assessed in the floor of the femoral triangle (Fig. 3). As the superficial Sartorius muscle crosses the ASIS (in the direction of the pes anserinus), the common tendon of the iliopsoas muscle will be located just medially from this point. When palpating further medially from the common tendon of the iliopsoas, one may feel a pulse, suggesting that the blood vessels inside the femoral triangle are being palpated. At these three palpation points, the therapists can confirm that they are in the correct location by asking the patient to raise their leg. The muscle contraction should be easy to palpate if the therapist is properly on the iliopsoas muscle.
Figure 2
Figure 2:
Modified Thomas test.
Figure 3
Figure 3:
The femoral triangle.

Two additional tests may be used to assess the iliopsoas muscle group: the flexion-adduction-internal rotation (FADIR) and skin rolling tests. Although these two tests are not commonly performed in those with potential iliopsoas involvement, the authors have found them to be useful.

The FADIR test is commonly used to assess those with FAIS and is found to have high sensitivity (0.94–0.99) but low specificity (0.05–0.09) (31). The FADIR test is performed with the patient supine and the therapist passively flexing, adducting, and then internally rotating the hip. In this position, the labrum can be pinched between the femoral head-neck junction and the acetabular rim. There are additional structures in the hip region that can be pinched with this test, including the iliopsoas tendon. Therefore, iliopsoas tension involvement needs to be considered when pain is reported during the FADIR test. If the patient complains of pain with the application of overpressure of normal motion, extraarticular soft tissue, including the common tendon of the iliopsoas, may be the source of impingement. However, if there is a significant loss of motion associated with pain and a firm or hard end-feel, the test results may indicate a mechanical problem in the hip joint, such as FAIS.

The second clinical evaluation test that the main author uses is the skin rolling test. As identified in the “trigger point map” (32), one of the referred points of the iliopsoas muscle is the low back. The skin rolling test is performed with the patient lying prone as the therapist grabs the skin and soft tissue around the patient's low back and roles the skin in the direction of the stiff soft tissue. The following can be observed with a positive skin rolling test: 1) reduced skin movement; 2) localized tenderness and erythema of the skin; and 3) stiffness of the soft tissue on the affected side. It is important to consider that the movement and elasticity of the patient's skin is largely genetic. Therefore, skin movement and elasticity must be compared on both sides of the lumbar spine. This skin rolling maneuver also may be used as a manual treatment technique, as described later.

Treatment

Physical therapy is the mainstay of treatment for those with iliopsoas syndrome, since most patients respond to conservative management (1). In this article, we will discuss conservative treatment solely, which includes manual therapy and active exercise.

Manual therapy

While several options exist for manual therapy techniques, the authors have found spine mobilization, strain counter strain, soft tissue mobilization directed at a trigger point, passive range of motion, contract-relax, and skin rolling to be effective.

Spine mobilization

Because the iliopsoas has an origin on the lumbar spine, manual treatment directed at the spine may help in those with muscle tightness and limited joint mobility. The first author recommends using a Maitland© posterior-anterior joint mobilization technique on the affected side. This may be done at the beginning of the treatment in an effort to loosen the affected iliopsoas muscle.

Strain counter strain

The strain counter strain technique, also known as positional release therapy, is performed by first having the therapist identify a tender trigger point in the affected muscle. A position that creates no tension on this point is used for treatment. The authors commonly position the patient supine with both knees flexed, legs crossed, and rested on the therapist's leg (Fig. 4). In this position, the therapist may combine other techniques, such as approximation, rotation of the hip, and deep breathing to assist in relaxation and pain reduction. After the pain decreases, the patient lies in this position for at least 90 s. The patient can use this position as a self-treating exercise by resting his or her legs on a chair or physioball at home.

Figure 4
Figure 4:
Strain counter strain position.

Trigger point treatment

Trigger points are defined as focal, hyperirritable spots located in a taut band of skeletal muscle. The spots are painful and can produce referred pain (33). There are some common methods to treat trigger points, such as massage therapy, sustained pressure, and transverse or rotation movement on the trigger point. During the irritable phase of an injury or in the first couple of weeks postsurgery, it is recommended to perform the technique with the muscle in a relaxed position. This position is typically with the patient lying supine, with his or her legs resting against the therapist's thigh (Fig. 5). In addition, the therapist can ask the patient to contract the gluteus maximus muscle to further relax the iliopsoas muscle through contract relax and activation of the antagonist muscle.

Figure 5
Figure 5:
Trigger points therapy position.

Friction therapy by hip movement

This technique has two versions. The first one is for patients with highly irritable pain. The patient lies supine with the hip positioned in 45 degrees of flexion and the feet placed on the treatment table. A mobilization belt is wrapped around the therapist's pelvis to laterally distract the patient's hip. The therapist places pressure on the trigger point while distracting the patient's hip laterally. In this technique, passive friction massage to the muscle is accomplished by the hip movement. For patients with less irritable pain, the authors recommend a more advanced technique. For this, the patient position changes to 90 degrees hip flexion with the feet being unsupported. In this position, the iliopsoas muscle will be activated. The therapist uses the belt, positioned as described above, to create a circumduction movement of the hip. Again, the friction massage is accomplished by the hip movement.

Soft tissue technique in a modified Thomas test

The first stage of this treatment method is suitable for patients with irritable pain. The patient is positioned as described in the modified Thomas test position with the affected limb off the edge of the table. A mobilization belt is secured to the patient's thigh and therapist so that the limb is supported and full hip extension is prevented. The therapist puts pressure on the trigger point with his/her thumb or thenar eminence while performing a contract-relax technique incorporating active hip flexion. The advantage of this technique is that the limb is supported in slight hip flexion with the iliopsoas muscle exposed. In this technique, there should be no stretching on the iliopsoas muscle.

To progress this technique for those patients with nonirritable pain, the patient's thigh is not supported with the mobilization belt. An advantage of using this contract-relax technique in the modified Thomas test position without support is that the iliopsoas muscle can be activated and stretched into extension through a full range of hip motion.

Skin rolling

The skin rolling treatment technique can be applied when skin rolling test results are positive. In this treatment, the therapist mobilizes the stiff tissue and rolls in the direction of the stiffness, typically present in the thorax and lumbar spine (Fig. 6). The purpose of this treatment is to make the tissue flexible and mobile. When choosing this technique, the therapist should be cautious in patients who have high pain irritability because this treatment technique may provoke pain.

Figure 6
Figure 6:
Skin rolling.

Active Exercise

Exercises to strengthen the iliopsoas muscle are not as commonly performed when compared with exercises directed at the gluteus medius, gluteus maximus, hamstrings, and/or quadriceps muscles. Perhaps, it is because there are some concerns that strengthening the iliopsoas could cause or aggravate hip pathology. Therefore, the authors are creative and cautious when prescribing exercises for the iliopsoas muscle. To diversify the exercise program, positions, leverage arms, and speed of movements are varied. Additionally, a combination of isometric, concentric, and eccentric exercises is used.

During the first stage of rehabilitation after injury, typically the first 2 wk, isometric exercises with isolated muscle contraction are recommend. Short leverage arm exercises also are recommended at this stage to avoid muscle overload and aggravation of symptoms. As symptoms subside, treatment can be progressed to more dynamic exercises with longer lever arms. These exercises combine coordination, core strength, and muscle balance. The exercises presented in this article are described in a progression of increased difficulty. The patient should be advanced during the rehabilitation period gradually; starting with the isometric exercise progressing along the continuum of exercises from concentric to eccentric over time as symptoms allow.

The average dosage of the exercise is presented in the Table. The therapist should make sure the patient performs each specific exercise with proper form at all times according to the dosage prescribed. When the patients are not in an irritable stage of pain, the exercise can be done with slight pain according to the pain monitoring model (34,35). This model suggests that during an exercise, pain is allowed to reach level 5 on the visual analog scale, where 0 is no pain and 10 is the worst pain imaginable. The patient should be aware that the pain should not increase during the exercise, and the pain should subside by the following day. In addition, the pain should not increase from week to week.

Table
Table:
The average dosage of exercise.

The therapist should be aware of contraindications and precautions when strengthening the iliopsoas muscle. This is especially true during the first few weeks following hip surgery or when working with a patient experiencing highly irritable pain. In the first author's experience, the patient should not begin iliopsoas isometric exercises for at least 4 wk (average time) after hip arthroscopy.

Isometric resistance exercise

For the isometric exercise, the patient lies supine with the affected hip in FABER while the heel rests on the flexed knee of the unaffected side. Resistance is applied to the thigh of the affected limb by either self-assisted or with an external force (Fig. 7). For the self-assisted exercises, resistance can be generated by the patient's hand. In this method, the resistance is self-controlled, typically less painful, and therefore, suitable for an a patient with irritable pain. The ipsilateral hand gives resistance to the affected limb in a direction that is parallel to the muscle fibers. The therapist can add manual resistance to the ankle dorsiflexors, to get a resistance similar to proprioceptive neuromuscular facilitation training. The exercises can be advanced so that the affected hip and knee are flexed to a 90-degree angle, without support from the unaffected limb. As illustrated in Figure 7, one can generate resistance by using a ball on the involved limb (e.g., a soccer ball or a basketball to associate the exercise with the patient's sport).

Figure 7
Figure 7:
Isometric resistance exercise.

Eccentric resistance exercise

Eccentric resistance can be performed with the patient supine and a resistance band around the feet. The exercise begins with both knees pulled toward the patient's chest. The unaffected limb is straightened while the patient uses both hands to support the affected limb. The patient can then slowly release his or her hands, thereby adding resistance to the affected hip. At first, the patient should try maintaining this position for 2 s using an isometric contraction. This exercise can be progressed so that the patient slowly extends the affected hip as he or she is resisting the band using an eccentric contraction of the iliopsoas. The therapist and patient should pay attention that the lumbar lordosis does not increase during this exercise. The technique is presented in supplemental video 1 (http://links.lww.com/CSMR/A55).

Hip flexion in quadruped

This exercise combines the contraction of the iliopsoas muscle with an addition of core activation. The patient is in a quadruped position with a resistance band wrapped around the patient's thighs. The exercise is performed by having the patient flex the hip against the resistance of the band. This technique is presented in supplemental video 2 (http://links.lww.com/CSMR/A56).

Hip flexion in high plank position

This exercise is an advanced version of the previous exercise with the patient in a high plank position and a resistance band around the patient's feet. The patient will flex the hip to activate the iliopsoas muscle. As mentioned earlier, the iliopsoas is considered a core muscle (18) and will be highly active during this exercise. This exercise also includes activation of the upper limbs, lower limbs, and trunk muscles. The technique is presented in supplemental video 3 (http://links.lww.com/CSMR/A57).

Reverse origin insertion sitting with a belt or with upper pulley

Because the iliopsoas originates from a large area in the lumbar spine and inserts in the lesser trochanter of the femur, when the patient extends his/her spine, activation of the iliopsoas may be less stressful as compared with the flexion of the hip. In this exercise, the patient sits with the affected hip positioned in FABER. The ankle rests on the knee of the unaffected limb. The patient needs to keep their torso straight and lean back slowly in a diagonal line while the foot of the affected limb pushes down toward the limb that is on the ground. This eccentric contraction is followed by a concentric contraction as the patient comes forward toward the affected limb to the starting upright position. In this exercise, the insertion of the muscle is fixed at the origin while the spine is moving with iliopsoas muscle activation. An advanced version of this exercise can be done with the affected hip fixed to an external object instead of resting on the unaffected leg. This position allows the iliopsoas to be active through a larger range of motion. The technique is presented in supplemental video 4 (http://links.lww.com/CSMR/A58).

Iliopsoas strength in half kneeling position

For this exercise, the patient kneels on a chair on the unaffected limb, with the knee of the affected limb flexed and a resistance band placed around both thighs. With the trunk upright and stabilized, the patient moves the affected limb from flexion to an extension, activating the iliopsoas through the desired range of motion. The patient should hold onto the back of a chair for support to emphasize the iliopsoas muscle activation. The exercises can be further progressed by performing the exercises while standing on an unstable surface, such as a balance pad. This technique is presented in supplemental video 5 (http://links.lww.com/CSMR/A59).

Hip flexor training with a resistance band (standing)

This exercise is inspired and similar to that used by Thorborg et al. (27). The results of their study showed a 17% increase in muscle strength after 6 wk of training. The exercise is performed in a standing position. Resistance is placed just above the patient's ankle. In this position, the patient performs a hip flexion movement against resistance. This exercise can be done emphasizing concentric, isometric, and/or eccentric types of muscle contractions. A sport-specific progression for soccer players can include combining the standing exercise with a kicking motion. The contractions can be altered by incorporating a high kicking motion and slow release, with a concentric contraction of 1 s and a longer eccentric contraction of 3 s. The technique is presented in supplemental video 6 (http://links.lww.com/CSMR/A60).

Standing on a BOSU with a straight leg

This is a functionally advanced exercise that includes iliopsoas strengthening, core activation, proprioception, balance, and motor control. The patient stands on a both sides up (BOSU) ball using one leg while performing functional or sport-specific tasks using the other leg. These sport-specific tasks should incorporate an iliopsoas muscle action, such as hip flexion and rotation of the limb over a hurdle, as presented in supplemental video 7 (http://links.lww.com/CSMR/A61). The affected and unaffected limbs can alternate as the stance leg on the BOSU ball depending on the goal of the exercise.

Dynamic, plyometric, and coordination exercises

In the late phase of rehabilitation, especially when athletes are able to return to their sport-specific training and practice, it is important to combine more dynamic, coordination related, and plyometric exercises for the iliopsoas. The therapist should be aware of the different dosage for plyometric-, dynamic-, and coordination-related exercises. Plyometric training is defined as high-velocity eccentric to concentric muscle loading (36,37) (e.g., jumping). The activity interval should be short, and the recovery time should be long. The literature recommends 3 to 5 or 9 to 12 repetitions per set with 3 or 4 sets per exercise (38,39). Based on the authors' experience, the dosage recommended is 3 sets of 10 repetitions of maximal force with each exercise and a long recovery time of 2 min. This is different than the dynamic and coordination exercises in which the activity time should approximately equal the recovery time. However, the therapist should consider the type of sports the patient participates in and base the time rest interval according to the demands of the specific sport. It is recommended to add resistance during these exercises as the patient advances. Resistance bands can be placed above the knees to best isolate resistance to the iliopsoas. Examples for this kind of exercise can be seen in supplemental videos 8 (http://links.lww.com/CSMR/A62) and 9 (http://links.lww.com/CSMR/A63).

Conclusion

The purpose of this article is to raise readers' awareness about impairments and pathology associated with the iliopsoas muscle group. Despite being essential for basic activities of daily living, as well as sports, it is often overlooked by clinicians. This may be because the iliopsoas muscle group is poorly understood, difficult to examine, and problematic to treat. There also is controversy related to the value of strengthening exercises directed at the iliopsoas muscle. A common misconception is that strengthening the iliopsoas muscle can harm the muscle and overload the hip joint. In addition, it is viewed by many that this muscle group is often shortened and treatment should focus only on stretching. However, strengthening this muscle group may be as important as strengthening any other muscle group. Based on clinical experience, a progression of strengthening exercises have been provided. More research is needed regarding the examination and rehabilitation of the iliopsoas muscle and its associated pathology. An area of particular interest should focus on exercises for the iliopsoas muscle group, including evidence to support the need for strengthening exercises, how best to perform exercises, and how to use exercises to manage associated pain.

The authors declare no conflict of interest and do not have any financial disclosures.

References

1. Tyler TF, Fukunaga T, Gellert J. Rehabilitation of soft tissue injuries of the hip and pelvis. Int. J. Sports Phys. Ther. [Internet]. 2014; 9:785–97. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25383247.
2. Tatu L, Parratte B, Vuillier F, et al. Descriptive anatomy of the femoral portion of the iliopsoas muscle. Anatomical basis of anterior snapping of the hip. Surg. Radiol. Anat. [Internet]. 2001; 23:371–4. Available from: https://www.ncbi.nlm.nih.gov/pubmed/11963618.
3. Christian N, Anderson MD. Iliopsoas. Clinics Sports Med. [Internet]. 2016; 35:419–33. Available from: https://www.clinicalkey.es/playcontent/1-s2.0-S0278591916300096. doi: 10.1016/j.csm.2016.02.009.
4. Philippon MJ, Devitt BM, Campbell KJ, et al. Anatomic variance of the iliopsoas tendon. Am. J. Sports Med. [Internet]. 2014; 42:807–11. Available from: https://journals.sagepub.com/doi/full/10.1177/0363546513518414.
5. Guerra DR, Reis FP, Bastos AA, et al. Anatomical study on the psoas minor muscle in human fetuses. Int. J. Morphol. [Internet]. 2012; 30:136–9. Available from: http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-95022012000100024&lng=en&tlng=en. Doi: 10.4067/S0717-950220120001000024.
6. Neumann DA, Garceau LR. A proposed novel function of the psoas minor revealed through cadaver dissection. Clin. Anatomy [Internet] 2015; 28:243–52. Available from: https://onlinelibrary.wiley.com/doi/abs/10.1002/ca.22467. Doi: 10.1002/ca.22467.
7. Fitzgerald P. The action of the iliopsoas muscle. Ir. J. Med. Sci. 1969; 2:31–3.
8. Ambegaonkar JP, Mettinger LM, Caswell SV, et al. Relationships between core endurance, hip strength, and balance in collegiate female athletes. Int. J. Sports Phys. Ther. [Internet]. 2014; 9:604–16. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25328823.
9. Andersson E, Oddsson L, Grundström H, Thorstensson A. The role of the psoas and iliacus muscles for stability and movement of the lumbar spine, pelvis and hip. Scand. J. Med. Sci. Sports. 1995; 5:10–6.
10. Dorn TW, Schache AG, Pandy MG. Muscular strategy shift in human running: dependence of running speed on hip and ankle muscle performance. J. Exp. Biol. [Internet]. 2012; 215(Pt 11):1944–56. Available from: https://www.ncbi.nlm.nih.gov/pubmed/22573774. Doi: 10.1242/jeb.064527, 215, 1944, 1956.
11. Mann RA, Moran GT, Dougherty SE. Comparative electromyography of the lower extremity in jogging, running, and sprinting. Am. J. Sports Med. 1986; 14:501–10.
12. Kellis E, Katis A. Biomechanical characteristics and determinants of instep soccer kick. J. Sports Sci. Med. [Internet]. 2007; 6:154–65. Available from: https://www.ncbi.nlm.nih.gov/pubmed/24149324.
13. Dörge HC, Andersen TB, Sørensen H, et al. EMG activity of the iliopsoas muscle and leg kinetics during the soccer place kick. Scand. J. Med. Sci. Sports. 1999; 9:195–200.
14. Serner A, Tol JL, Jomaah N, et al. Diagnosis of acute groin injuries. Am. J. Sports Med. [Internet]. 2015; 43:1857–64. Available from: https://journals.sagepub.com/doi/full/10.1177/0363546515585123. Doi: 10.1177/0363546515585123.
15. Redmond JM, Gupta A, Hammarstedt JE, et al. The hip-spine syndrome: how does back pain impact the indications and outcomes of hip arthroscopy? Arthroscopy [Internet]. 2014; 30:872–81. Available from: https://www.clinicalkey.es/playcontent/1-s2.0-S0749806314001704.
16. Gebhart JJ, Weinberg DS, Conry KT, et al. Hip-spine syndrome: is there an association between markers for cam deformity and osteoarthritis of the lumbar spine? Arthroscopy [Internet]. 2016; 32:2243–8. Available from: https://www.clinicalkey.es/playcontent/1-s2.0-S0749806316301992. doi: 10.1016/j.arthro.2016.04.025.
17. Weinberg D, Xie K, Liu R, et al. Increased pelvic incidence is associated with a more coronal facet orientation in the lower lumbar spine: a cadaveric study of 599 lumbar spines. Spine [Internet]. 2016; 41:E1145. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27031765. doi: 10.1097/BRS.0000000000001577, 41, E1138, E1145.
18. Weng W, Wu H, Wu M, et al. The effect of total hip arthroplasty on sagittal spinal-pelvic-leg alignment and low back pain in patients with severe hip osteoarthritis. Eur. Spine J. [Internet]. 2016; 25:3608–14. Available from: https://www.ncbi.nlm.nih.gov/pubmed/26883265. Doi: 10.1007/s00586-016-4444-1, 25, 3608, 3614.
19. Prather H, Cheng A, Steger-May K, et al. Hip and lumbar spine physical examination findings in people presenting with low back pain, with or without lower extremity pain. J. Orthop. Sports Phys. Ther. [Internet]. 2017; 47:163–72. Available from: https://www.ncbi.nlm.nih.gov/pubmed/28158964. doi: 10.2519/jospt.2017.6567, 47, 163, 172.
20. Hicks GE, Sions JM, Velasco TO. Hip symptoms, physical performance, and health status in older adults with chronic low back pain: a preliminary investigation. Arch. Phys. Med. Rehabil. [Internet]. 2018; 99:1273–8. Available from: https://www.sciencedirect.com/science/article/pii/S0003999317312881. doi: 10.1016/j.apmr.2017.10.006.
21. Miyagi M, Fukushima K, Inoue G, et al. Hip-spine syndrome: cross-sectional-study of spinal alignment in patients with coxalgia. HIP Int. [Internet]. 2019; 29:21–5. Available from: https://journals.sagepub.com/doi/full/10.1177/1120700018803236. doi: 10.1177/1120700018803236.
22. Watelain E, Dujardin F, Babier F, et al. Pelvic and lower limb compensatory actions of subjects in an early stage of hip osteoarthritis. Arch. Phys. Med. Rehabil. 2001; 82:1705–11.
23. Gómez-Hoyos J, Martin R, Martin H. Current concepts review: evaluation and management of posterior hip pain. J. Am. Acad. Orthop. Surg. [Internet]. 2018; 26:597–609. Available from: https://www.ncbi.nlm.nih.gov/pubmed/30080760. doi: 10.5435/JAAOS-D-15-00629, 26, 597, 609.
24. Moreside J, Wong I, Rutherford D. Altered erector spinae activity and trunk motion occurs with moderate and severe unilateral hip OA. J. Orthop. Res. [Internet]. 2018; 36:1826–32. Available from: https://onlinelibrary.wiley.com/doi/abs/10.1002/jor.23841. doi: 10.1002/jor.23841.
25. Bogduk N, Pearcy M, Hadfield G. Anatomy and biomechanics of psoas major. Clin. Biomech. 1992; 7:109–19.
26. Avrahami D, Potvin JR. The clinical and biomechanical effects of fascial-muscular lengthening therapy on tight hip flexor patients with and without low back pain. J. Can. Chiropr. Assoc. [Internet]. 2014; 58:444–55. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25550670.
27. Thorborg K, Bandholm T, Zebis M, et al. Large strengthening effect of a hip-flexor training programme: a randomized controlled trial. Knee Surg. Sports Traumatol. Arthrosc. [Internet]. 2016; 24:2346–52. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25796586. doi: 10.1007/s00167-015-3583-y, 24, 2346, 2352.
28. Werner J, Hägglund M, Walden M, Ekstrand J. UEFA injury study: a prospective study of hip and groin injuries in professional football over seven consecutive seasons. Br. J. Sports Med. [Internet]. 2009; 43:1036–40. DOI: 10.1136/bjsm.2009.066944.
29. Heyworth BE, Shindle MK, Voos JE, et al. Radiologic and intraoperative findings in revision hip arthroscopy. Arthroscopy [Internet]. 2007; 23:1295–302. Available from: https://www.clinicalkey.es/playcontent/1-s2.0-S0749806307009619.
30. Dennis RJ, Finch CF, Elliott BC, Farhart PJ. The reliability of musculoskeletal screening tests used in cricket. Phys. Ther. Sport [Internet]. 2007; 9:25–33. Available from: https://www.clinicalkey.es/playcontent/1-s2.0-S1466853X07000983.
31. Reiman MP, Goode AP, Cook CE, et al. Diagnostic accuracy of clinical tests for the diagnosis of hip femoroacetabular impingement/labral tear: a systematic review with meta-analysis. Br. J. Sports Med [Internet]. 2015; 49:811. Available from: http://dx.doi.org/10.1136/bjsports-2014-094302.
32. Simones D, Travel J, Simons L. Myofascial Pain and Dysfunction the Trigger Point Manual. 2nd ed. Butler J, editor. Philadelphia (PA): Lippincott Williams & Wilkins; 1993. p. 90.
33. Alvarez DJ, Rockwell PG. Trigger points: diagnosis and management. Am. Fam. Phys. [Internet]. 2002; 65:653–60. Available from: https://www.ncbi.nlm.nih.gov/pubmed/11871683.
34. Silbernagel KG, Thomeé R, Eriksson BI, Karlsson J. Continued sports activity, using a pain-monitoring model, during rehabilitation in patients with Achilles tendinopathy. Am. J. Sports Med. [Internet]. 2007; 35:897–906. Available from: https://journals.sagepub.com/doi/full/10.1177/0363546506298279.
35. Thomeé R. A comprehensive treatment approach for patellofemoral pain syndrome in young women. Phys. Ther. 1997; 77:1690–703.
36. Voight M. Stretch strengthening: an introduction to plyometrics. Orthop. Phys. Ther. Clin North Am. 1992; 1:243–52.
37. Kisner C, Allen L. Therapeutic Exercise Foundations and Techniques. 5th ed. Pine JA editor. Philadelphia (PA): F.A Davis Company; 2007. p. 208–10.
38. Lesinski M, Prieske O, Granacher U. Effects and dose-response relationships of resistance training on physical performance in youth athletes: a systematic review and meta-analysis. Br. J. Sports Med [Internet]. 2016; 50:781–95. Available from: http://dx.doi.org/10.1136/bjsports-2015-095497.
39. Rio E, Kidgell D, Pudram C, et al. Isometric exercise induces analgesia and reduces inhibition in patellar tendinopathy. Br. J. Sport Med [Internet]. 2015; DOI: 10.1136/bjsports-2014-094386.

Supplemental Digital Content

Copyright © 2020 by the American College of Sports Medicine