Evidence-Based Strength Training: Gluteus Maximus

To build upon my previous post regarding Evidence-based Strength Training of the Gluteus Medius, I wrote the following article for MedBridge Education

Pain and Gluteal Strength

The gluteal musculature has been implicated in many different pathologies due to its potential impact on lower extremity biomechanics. During weight bearing, the femur moves about a fixed patella and therefore excessive femoral internal rotation and adduction results in increased contact directed primarily at the lateral facet of the patella1. Just 10° of IR can lead to a substantial decrease in PFJ contract area and a 50% increase in joint stress. Coinciding with these findings, Souza et al.2 found that females with patellofemoral pain syndrome (PFPS) demonstrated greater peak hip internal rotation compared to the control group during running, drop jump, and step down. The PFPS group also demonstrated 14% weaker hip abductor strength and 17% weaker hip extensor strength. Wilson et al3, Noehren et al4, and Nakagawa et al5 found that individuals presenting with PFPS demonstrated increased hip adduction during running, jumping, and single-leg squats. This excess femoral adduction creates an increased valgus force about the knee joint, which in turn causes increased loading of the lateral patellofemoral joint. In addition to patellofemoral pain, a hip etiology or influence has also been implicated in iliotibial band syndrome6, anterior cruciate ligament rupture7, and achilles tendinopathy8. More specifically, impaired gluteus maximus function has been demonstrated in individuals diagnosed with femoroacetabular impingement9.

Gluteal strengthening and Rehabilitation

In support of a gluteal etiology, several studies have found the effectiveness of gluteal strengthening in the treatment of lower extremity disorders. A recent systematic review conducted by Santos and colleagues9 found gluteal strengthening decreased the highest intensity of pain experienced during the previous week, pain when ascending and descending stairs, and pain while squatting or sitting for prolonged periods amongst individuals diagnosed with PFPS. Additionally, with regards to rehabilitation following anterior cruciate ligament reconstruction, the inclusion of hip strengthening appears to improve sagittal plane dynamic balance at three months post ACLR as compared to traditional rehabilitation10.

EMG Activity and Exercise Goals

According to Reiman et al.11 and Escamilla et al.12, moderate electromyographic activity (EMG) activation (21-40% MVIC) is best used to facilitate endurance and neuromuscular re-education; high activation (41-60+% MVIC) in order to promote strength gains.

From Biomechanics to Exercises

Gluteus Maximus

Origin: Ilium posterior to posterior gluteal line; dorsal surface of sacrum and coccyx; sacrotuberous ligament

Insertion: Iliotibial tract and gluteal tuberosity

Primary Function: Extends thigh and assists in hip abduction and external rotation; steadies thigh and assists in rising from sitting position

Among introductory exercises, the gluteus maximus achieves the highest EMG levels during:

  1. Front-plank with Hip Extension
  2. Gluteal Squeeze
  3. Side-plank with Hip Abduction
  4. Quadruped with Contralateral Arm/Leg Lift
  5. Uni-lateral Bridge

screen-shot-2016-09-19-at-2-51-18-pm

Additionally, you must consider the interaction of other muscles acting with or against the gluteus maximus when determining exercise prescription. It has been proposed that individuals who demonstrate excess femoral internal rotation during functional tasks may be relying too heavily on the tensor fasciae latae to control their pelvis in the presence of weak or inhibited gluteus medius musculature.

Selkowitz and colleagues determined that the following exercises achieved the best Gluteal to Tensor Fasciae Latae Activation Ratio:

  1. Clamshell
  2. Side-step with resistance band
  3. Single-leg bridge
  4. Quadruped hip extension with knee extended
  5. Quadruped hip extension with knee flexed

screen-shot-2016-09-19-at-2-55-12-pm

Finally, when progressing your patient towards more functional closed kinetic chain and sport/activity-specific exercises, the following exercises achieve the highest gluteus medius activation:

  1. Cross-over Step-up
  2. Hip Thrust Variations (Barbell, Band, American)
  3. Rotational Single-Leg Squat
  4. Skater Squat
  5. Single-Leg Squat

screen-shot-2016-09-19-at-2-56-43-pm

Exercise prescription is a multi-faceted decision, which is driven by the individual patient’s goals, functional limitations, and the evidence supporting the treatment of these factors. Using EMG studies to drive the selection of exercise is highly valuable, especially during early stages of rehabilitation or when attempting to isolate individual muscles and/or groups of muscles. However, there are limitations when comparing different studies due to methodological differences (type of EMG, patient population, data analysis, etc.). Additionally, due to the cost and time to conduct these studies, there are thousands of exercises that have not been evaluated in the literature. In light of this information, these studies should be used to guide your decision making, it should not override your clinical expertise when accompanied by biological plausibility.

VMO: An Update

The following is an article written for the online, video-based physical therapy continuing education company MedBridge

Patellofemoral pain syndrome (PFPS) is among the most common sports injuries and yet the current treatment protocols are not optimal. In particular, the latest research questions our ability to selectively recruit vastus medialis obliquus (VMO) and affect its timing and suggests that VMO may have nothing to do with the PFPS.

Prevalence of Patellofemoral Pain Syndrome

PFPS has an astounding prevalence according to a retrospective case-control analysis by Taunton et al. They analyzed 2,002 running-related injuries seen at a primary care sports injury facility – and 42.1% (842/2,002) were knee injuries. Of these knee injuries, 39.3% (331/842) were due to patellofemoral pain syndrome (PFPS), which made PFPS by far the most common diagnosis found in this large-scale study.

Similarly, in an older study (1984), Devereaux et al found that over a five year period, 137 patients presented with PFPS – accounting for 25% of all knee injuries seen at this sports injury clinic.

These two studies were conducted 17 years apart, giving support to the consistently high prevalence of this disorder. Now the most important question is, how are we treating these patients?

How are we treating patients with PFPS?

Imbalance of LV and VMO

The biomechanical study by Lieb et al made the VMO the mainstay of most physical therapy protocols and treatment approaches for PFPS.

Conducted in 1968, the study found that VMO’s fibers are oriented at 55° from the longitudinal axis of the femur. This orientation alone makes VMO the primary restraint to lateral subluxation of the patella. The study further postulated that VMO was able to counterballance the pull of the much larger vastus lateralis (VL) due to the discrepancy in mechanical advantages.

As a result of this study, an insufficient balance between the VL and VMO has long been considered the primary contributing factor in developing patellar subluxation, or maltracking.

VL:VMO timing

A study by Cowan et al found that subjects with PFPS have an imbalance of VL:VMO timing. The VL typically begins to fire approximately 15-20 ms prior to the VMO.

Due to this understanding of the biomechanics, the treatment strategy typically involved correcting the potential VMO atrophy, hypoplasia, inhibition, and impaired motor control.

Now, this all seems logical in theory, but can we actually selectively train the VMO? Is this relatively small muscle affected differently than the rest of the quadriceps musculature in the presence of pain?

New research questions…

Does VMO atrophy relative to the rest of quadriceps?

A recent study by Giles and colleagues refutes one of the cornerstones of the VMO theory; namely, that this small muscle tends to atrophy relative to the rest of the quadriceps during or following surgery. They performed a cross-sectional study of 35 participants diagnosed with PFPS.

The results showed atrophy of all portions of the quadriceps muscles – and no selective atrophy of the VMO – present in the affected limb of people with unilateral PFPS.

Can we selectively activate VMO?

Even if the atrophy was present, the literature is not very kind to the ability to preferentially activate this musculature either.

Cerny et al evaluated the ability to preferentially recruit the VMO during 22 different quadriceps exercises. Through electromyographic analysis, they determined that VMO activity was not higher in any exercise compared to VL.

In a randomized controlled trial, Song et al found no evidence that VMO can be activated separately. They compared the change in VMO cross-sectional area after 8 weeks of unilateral leg press and unilateral leg press with subsequent hip adduction. The two groups showed no significant difference between the change in VMO cross-sectional area (the standard leg press actually yielded better results).

Thus, selective isolation of the VMO in everyday clinical practice is highly unlikely. In all reality, if we consider inability to selectively recruit their target, most of the ‘VMO programs’ are merely strengthening the quadripceps as a whole. If we could selectively recruit these fibers, according to Grabiner et al, it would take approximately 60% of maximal voluntary contraction to stimulate hypertrophy of the VMO.

Does VMO training have advantages over general quadriceps strengthening?

In 2010, Bennell et al investigated how VMO retraining compares to a general quadriceps strengthening program in relation to vasti onset.

The VMO retraining group used EMG biofeedback during the following series of exercises:

  • isometric VMO contractions at 90° of knee flexion
  • standing mini squats to 40°
  • isometric contraction of the VMO in combination with hip abduction and hip external rotation during an isometric wall contraction in standing
  • step downs

The quadriceps group performed:

  • isometric quad sets
  • straight-leg raises
  • SAQs
  • side-lying hip abduction

At the conclusion of the training programs, the retraining group actually did create more significant changes in stair descent activation in the short-term. However, at the 8-week follow-up, both values were nearly identical. The initial improvement may have been due to the use of ‘step downs’ in the retraining group, which most closely simulates the functional and muscular demands of stair descent.

During stair ascent, on the other hand, the quadriceps strengthening group caused a much more significant alteration in VMO:VL timing and was the only group that caused the VMO to fire prior to the VL.

A study conducted by Laprade et al showed similar results using isometric exercise. This study compared the EMG activity in individuals with PFPS and asymptomatic controls during 5 isometric exercises. There was no significant difference in the ratio of VMO:VL firing between the two groups.

Given these results, I find it hard to support the use of VMO training in everyday clinical practice.

Does VMO strengthening make a difference for PFPS?

Suppose it was possible to selectively recruit the VMO. Would it reduce patellofemoral contact stress sufficiently to relieve the pain?

Sawatsky et al say no. They conducted a biomechanical study using New Zealand white rabbits. Although this is not a direct human study, the muscular alignment and pull of the quadriceps is very similar: the fibers of the VMO and VL are oriented at 45-50° and 14-19°, respectively, in relation to the longitudinal axis of the femur.

They transected VMO at varying levels of knee flexion (30°, 60°, and 90°), measuring patellofemoral joint contact pressures before and after the transections.

There were no significant differences between peak pressures, average pressures, contact areas, or contact shapes before and after transection.

If the contact area and pressure are not altered when the muscle is removed from the equation, then why do we continue thinking VMO training is the gold standard in PFPS treatment?

Evidence-Based Strength Training: Gluteus Medius, An Update

To build upon my previous post regarding Evidence-based Strength Training of the Gluteus Medius, I wrote the following article for MedBridge Education

Pain and Gluteal Strength

The gluteal musculature has been implicated in many different pathologies due to its potential impact on lower extremity biomechanics. During weight bearing, the femur moves about a fixed patella and therefore excessive femoral internal rotation and adduction results in increased contact directed primarily at the lateral facet of the patella1. Just 10° of IR can lead to a substantial decrease in PFJ contract area and a 50% increase in joint stress. Coinciding with these findings, Souza et al.2 found that females with patellofemoral pain syndrome (PFPS) demonstrated greater peak hip internal rotation compared to the control group during running, drop jump, and step down. The PFPS group also demonstrated 14% weaker hip abductor strength and 17% weaker hip extensor strength. Wilson et al3, Noehren et al4, and Nakagawa et al5 found that individuals presenting with PFPS demonstrated increased hip adduction during running, jumping, and single-leg squats. This excess femoral adduction creates an increased valgus force about the knee joint, which in turn causes increased loading of the lateral patellofemoral joint. In addition to patellofemoral pain, a hip etiology or influence has also been implicated in iliotibial band syndrome6, anterior cruciate ligament rupture7, and achilles tendinopathy8.

Gluteal strengthening and Rehabilitation

In support of a gluteal etiology, several studies have found the effectiveness of gluteal strengthening in the treatment of lower extremity disorders. A recent systematic review conducted by Santos and colleagues9 found gluteal strengthening decreased the highest intensity of pain experienced during the previous week, pain when ascending and descending stairs, and pain while squatting or sitting for prolonged periods amongst individuals diagnosed with PFPS. Additionally, with regards to rehabilitation following anterior cruciate ligament reconstruction, the inclusion of hip strengthening appears to improve sagittal plane dynamic balance at three months post ACLR as compared to traditional rehabilitation10.

EMG Activity and Exercise Goals

According to Reiman et al.11 and Escamilla et al.12, moderate electromyographic activity (EMG) activation (21-40% MVIC) is best used to facilitate endurance and neuromuscular re-education; high activation (41-60+% MVIC) in order to promote strength gains.

From Biomechanics to Exercises

Gluteus Medius

Origin: External surface of Ilium between anterior and posterior gluteal lines

Insertion: Lateral surface of greater trochanter

Primary Function: Abduction of the hip joint; the anterior fibers contribute to hip flexion and hip internal rotation, and the posterior fibers to hip extension and hip external rotation. Additionally, the gluteus medius is responsible for preventing the opposite side of the pelvis from dropping during the stance phase of gait and plays a major role in providing frontal stability for the entire pelvis during walking and other functional activities.

The gluteus medius achieves the highest EMG levels during13,14:

  1. Side-lying plank with hip abduction
  2. Reverse clamshell with hip abduction and extension
  3. Prone plank with hip extension
  4. Reverse clamshell with hip abduction
  5. Single-leg Bridge

Screen Shot 2015-07-26 at 3.30.35 PM

Additionally, you must consider the interaction of other muscles acting with or against the gluteus medius when determining exercise prescription. It has been proposed that individuals who demonstrate excess femoral internal rotation during functional tasks may be relying too heavily on the tensor fasciae latae to control their pelvis in the presence of weak or inhibited gluteus medius musculature.

Selkowitz and colleagues determined that the following exercises achieved the best Gluteal to Tensor Fasciae Latae Activation Ratio15:

  1. Clamshell
  2. Side-step with resistance band
  3. Single-leg bridge
  4. Quadruped hip extension with knee extended
  5. Quadruped hip extension with knee flexed

Screen Shot 2015-07-26 at 3.23.48 PM

Finally, when progressing your patient towards more functional closed kinetic chain and sport/activity-specific exercises, the following exercises achieve the highest gluteus medius activation13,16,17,18:

  1. Walking lunge with dumbbell in contralateral hand
  2. Unilateral mini-squat
  3. Skater squat
  4. Unilateral deadlift
  5. Unilateral wall squat

Screen Shot 2015-07-26 at 3.24.37 PM

Exercise prescription is a multi-faceted decision, which is driven by the individual patient’s goals, functional limitations, and the evidence supporting the treatment of these factors. Using EMG studies to drive the selection of exercise is highly valuable, especially during early stages of rehabilitation or when attempting to isolate individual muscles and/or groups of muscles. However, there are limitations when comparing different studies due to methodological differences (type of EMG, patient population, data analysis, etc.). Additionally, due to the cost and time to conduct these studies, there are thousands of exercises that have not been evaluated in the literature. In light of this information, these studies should be used to guide your decision making, it should not override your clinical expertise when accompanied by biological plausibility.

Should we stop blaming the glutes for everything?

Below is an article written for MikeReinold.com… 

Anterior cruciate ligament (ACL) rupture1,2 and patellofemoral pain syndrome (PFPS)3,4,5 are two of the most common lower extremity complaints that physicians or physical therapists will encounter. In addition to the high incidence of these pathologies, with regards to ACL injury, very high ipsilateral re-injury and contralateral injury have also been reported6,7,8. With the importance of treating and/or preventing these injuries, several researchers have taken it upon themselves to determine what movement patterns predispose athletes to developing these injuries. This research indicates that greater knee abduction moments9,10, peak hip internal rotation11 and hip adduction motion12 are risk factors for PFPS development. Whereas, for ACL injury, Hewett and colleagues13 conducted a prospective cohort study identifying Knee abduction angle at landing as predictive of injury status with 73% specificity and 78% sensitivity. Furthermore, as the risk factors for developing both disorders are eerily similar, Myer et al performed a similar prospective cohort study finding that athletes demonstrating >25 Nm of knee abduction load during landing are at increased risk for both PFPS and ACL injury14. With a fairly robust amount of research supporting a hip etiology in the development of these injuries, it would make sense that weakness of the hip musculature would also be a risk factor, right?

A recent systematic review found very conflicting findings on the topic. With regards to cross-sectional research, the findings were very favorable with moderate level evidence indicating lower isometric hip abduction strength with a small effect size (ES) and lower hip extension strength with a small ES15. Additionally, there was a trend toward lower isometric hip external rotation and moderate evidence indicates lower eccentric hip external rotation strength with a medium ES in individuals with PFPS15. Unfortunately, the often more influential prospective evidence told a different story. Moderate-to-strong evidence from three high quality studies found no association between lower isometric strength in hip abduction, extension, external rotation or internal rotation and the risk of developing PFPS15. The findings of this systematic review indicated hip weakness may be a potential consequence of PFPS, rather than the cause. This may be due to disuse or fear avoidance behaviors secondary to the presence of anterior knee pain. Regardless of its place as a cause or consequence, hip strengthening has proved beneficial in patients with both PFPS16,17,18 and following ACL Reconstruction19, but does it actually help to change the faulty movement patterns?

Gluteal strengthening can cause several favorable outcomes, from improved quality of life to decreased pain, unfortunately however marked changes in biomechanics is not one of the benefits. Ferber and colleagues20 performed a cohort study analyzing the impact of proximal muscle strengthening on lower extremity biomechanics and found no significant effect on two dimensional peak knee abduction angle. In slight contrast however, Earl and Hoch21 found a reduction in peak internal knee abduction moment following a rehabilitation program including proximal strengthening, but no significant change in knee abduction range of motion was found. It should be noted that this study included strengthening of all proximal musculature and balance training, so its hard to conclude that the results were due to the strengthening program. Potentially, gluteal endurance may be more influential than strength itself, so it would make sense that following isolated fatigue of this musculature, lower extremity movement patterns would deteriorate.

Once again, this belief is in contrast to the available evidence. While fatigue itself most definitely has an impact on lower extremity quality of movement, isolated fatigue of the gluteal musculature tells a different story. Following a hip abductor fatigue protocol, patients only demonstrated less than a one degree increase in hip-abduction angle at initial contact and knee-abduction angle at 60 milliseconds after contact during single-leg landings22. In agreement with these findings, Geiser and colleagues performed a similar hip abductor fatigue protocol and found very small alterations in frontal plane knee mechanics, which would likely have very little impact on injury risk23. The biomechanical explanation for why weakness or motor control deficits in the gluteal musculature SHOULD cause diminished movement quality makes complete sense, but unfortunately, the evidence at this time does not agree.

While the evidence itself does not allow the gluteal musculature to shoulder all of the blame, this does not mean we should abandon addressing these deficits in our patients. As previously stated, posterolateral hip strengthening has multiple benefits, but it is not the end-all-be-all for rehabilitation or injury prevention of lower extremity conditions. Proximal strength deficits should be assessed through validated functional testing in order to see its actual impact on lower extremity biomechanics on a patient-by-patient basis. Following this assessment, interventions should be focused on improving proximal stability, movement re-education, proprioception, fear avoidance beliefs, graded exposure, and the patient’s own values, beliefs, and expectations.

Evidence-Based Strength Training: Scapulothoracic Musculature, Part 2

Scapulothoracic Muscles and Pain

As I mentioned in Part 1, weakness or poor neuromuscular control of the periscapular muscles has been implicated in subacromial impingement1,2, lateral epicondylalgia3-5, cervicogenic headache6, and neck pain7,8.

Specifically, insidious onset of neck pain and whiplash associated disorder (WAD) have been linked with a significant delay in and shorter duration of serratus anterior activity bilaterally during arm elevation9. A similar study found decreased serrates anterior activation in individuals with acromioclavicular osteoarthritis and rotator cuff disease.10

Although a cause-and-effect relationship cannot be confirmed, this preliminary evidence still lends support for targeting the periscapular muscles in individuals with neck or shoulder pain.

EMG Activity and Exercise Goals

According to Reiman et al.11 and Escamilla et al.12, moderate EMG activation (21-40% MVIC) is best used to facilitate endurance and neuromuscular re-education; high activation (41-60+% MVIC) – to promote strength gains.

From Biomechanics to Exercises

Serratus Anterior

Primary Function: scapular upward rotation, external rotation, posterior tilt at the acromioclavicular joint, protraction of the clavicle at the sternoclavicular joint.

Origin: External surfaces of lateral aspect of 1st-8th ribs

Insertion: Anterior surface of medial border of scapula

The SA is often activated with scapular protraction. The exercises yielding the highest MVIC for the serratus anterior include:

  • dynamic hug13
  • push-up plus13
  • scaption with external rotation14
  • diagonal PNF (shoulder flexion, horizontal flexion, external rotation)15
  • shoulder abduction in scapular plane above 120 degrees15

The upper trapezius (UT) often compensates for a weak or inhibited serratus anterior, so it’s beneficial to selectively activate the SA in lieu of the UT. According to Cools and colleagues, the best SA:UT ratio is achieved in:

  • high row
  • forward shoulder flexion
  • scaption with external rotation14
Serratus Anterior
Prone Push Up with Plus
Serratus Anterior
Dynamic Hug with Resistance
[Table] MVIC values for SA exercises

Levator Scapulae

Primary Functions: scapular elevation, glenoid cavity inferior tilt through upward scapular rotation

Origin: Posterior tubercles of transverse processes of C1-C4 vertebrae

Insertion: Medial border of scapula superior to root of scapular spine

These muscles have received little attention in the literature compared the SA or trapezius. In a study, Moseley and colleagues discovered that the levator scapulae achieves the highest activity in:

  • rowing
  • horizontal abduction
  • shrug
  • horizontal abduction with ER
  • prone shoulder extension16
[Table] MVIC values for Levator Scapulae exercises

Rhomboids

Primary Functions: Retraction of the scapula; upward rotation to depress glenoid cavity; scapular attachment to thoracic wall

Origin: nuchal ligament; spinous processes of C7, T1 and T2-T5 vertebrae

Insertion: smooth triangular area at medial end of scapular spine; medial border of scapula from level of spine to inferior angle

The rhomboids achieve the highest MVIC during:

  • ER at 90° of abduction17
  • ER at 0° of abduction17
  • horizontal abduction16
  • shoulder extension17
  • scaption16
Levator Scapulae
Prone Shoulder Row
Rhomboid
Shoulder External Rotation at 90° Abduction with Dumbbell
[Table] MVIC values for rhomboid muscle exercises

Choosing the Best Exercise

These studies give us a glimpse into properly selecting exercises, yet very few exercises have been or will ever be studied.

When choosing an exercise for your patient, be sure to consider:

  • the biomechanics of the movement,
  • current evidence for or against the exercise,
  • your patient’s presentation, and goals for treatment.
  • aggravating movement(s) or comparable signs

Evidence-Based Strength Training: Rotator Cuff

This will be the first in a series of monthly posts that I will be contributing to MedBridge Education, who is an online continuing education resource for physical and occupation therapists…

According to Sipes et al, 30% of athletes suffer a shoulder injury during their career. Of those injuries, subacromial impingement syndrome and rotator cuff tendonitis were the most common shoulder injuries for each individual sport and accounted for 27% and 24% of total shoulder injuries, respectively. More specifically, over-head throwing athletes are especially susceptible to shoulder pathology as 28% of all injuries in professional baseball have been shown to occur at the shoulder (Cante et al).

Additionally, van der Windt et al conducted a prospective evaluation of over 300 patients. This analysis found that approximately 48% of shoulder injuries in a general population were diagnosed as subacromial impingement. Stability at the glenohumeral joint is dependent upon the passive stabilization of the ligamentous tissues and the dynamic stability provided by the rotator cuff musculature, as well as indirectly by the stability of the scapula and the muscles that support it. The rotator cuff’s primary role is to center the humeral head in the glenoid fossa, which requires adequate muscular strength and endurance. Because the rotator cuff muscles all originate from the scapula, appropriate functional control of the scapula is also an important rehab target.

As weakness of the rotator cuff and scapular stabilizing musculature can predispose individuals to subsequent pathological conditions, understanding what exercises are most effective in training these muscles is of utmost importance to the practicing clinician and student alike.  Evidence supports the use of appropriate exercises and manual therapy to improve the strength and function of these muscles. For example, in a clinical trial (Bang et al) comparing an exercise program to the same program with the addition of manual therapy, strength of patients in the manual therapy program improved significantly whereas the exercise-only group did not. In addition, based on the unique ROM, capsular laxity, strength, proprioception, and osseous anomalies specific to the over-head athlete, they too require the creation of a rehabilitation program specific to the demands of their sport/position (see: “Rehabilitation of the Overhead Throwing Athlete”). This review will touch on strength training interventions targeting the rotator cuff, but please remember this is only the tip of the iceberg in terms of rehabilitative principles.

Supraspinatus:

The supraspinatus originates from the supraspinous fossa and inserts laterally to the superior facet of the greater tubercle of the humerus. Based on this muscle’s line of pull, its primary responsibility involves concentric abduction of the humerus. In addition to this primary action, the supraspinatus also drives the superior roll of the humeral head and compresses the humeral head firmly against the glenoid fossa during shoulder abduction. Secondarily, this muscle contributes a small external rotation torque. Supraspinatus mm Based on these biomechanical and anatomical considerations, Reinold et al investigated the electromographic (EMG) activity of the supraspinatus through  three common therapeutic exercises, which also serve as diagnostic tests for shoulder impingement when performed isometrically (Full Can, Empty Can , and Prone Full Can). All three of these exercises had nearly identical EMG data ranging between 62% (Full Can) and 67% Maximal Voluntary Isometric Contraction (MVIC) (Prone Full Can). It should also be noted that there was significantly greater middle and posterior deltoid EMG activity during the empty can exercise, which can contribute to superior humeral head migration and a predisposition to subacromial impingement. Biomechanically speaking, when the humerus is elevated in a position of internal rotation, it does not allow the greater tuberosity to clear from under the acromion as it does in a neutral or externally rotated position. Based on these findings, why are we still using the more provocative Empty Can when the better tolerated full can exercise is just as effective? The answer for this is still unclear.

Earlier in 2004, Reinold et al conducted a similar study looking at a broader range of exercises and muscular contributions of the supraspinatus, infraspinatus, teres minor, and posterior & middle deltoid. It was determined that the top three exercises based on %MVIC were Prone Horizontal Abduction at 100° with full external rotation (82% MVIC), Prone External Rotation at 90° of abduction (68% MVIC), and Standing External Rotation at 90° of abduction (57% MVIC). As previously stated, selecting exercises that activate the supraspinatus while minimizing the activity of the deltoid musculature is of importance in the rehabilitation of most shoulder pathologies. This information could make utilizing the Prone Horizontal Abduction at 100° with Full External Rotation and Prone External Rotation at 90° of abduction detrimental to proper rehabilitation as substantial deltoid activity was recorded at 82% and 79% MVIC, respectively.

In lieu of this additional consideration, the most appropriate exercises for isolated strengthening of the supraspinatus are the Full Can, Prone Full Can, and Side-lying ER (51% MVIC). Once progressing to a more functional program targeting scapular and glenohumeral stability, it must be noted that this does not necessarily warrant the discharge of more targeted rotator cuff exercises in favor of seemingly more difficult weight-bearing exercises. Uhl et al evaluated several common weight-bearing exercises and of the exercises evaluated, the most intensely the supraspinatus was engaged was only 29% MVIC during a single-arm push-up.

Infraspinatus:

The infraspinatus originates distally to the supraspinatus at the infraspinous fossa of the scapula and attaches laterally at the middle facet of greater tubercle of the humerus. Based on this muscle’s origin and insertion, its primary action involves external rotation of the humerus. Infraspinatus mm. The secondary actions of the infraspinatus include horizontal abduction, glenohumeral compression at the glenoid fossa, and resistance to superior and anterior humeral head translation. This is why many diagnostic special tests for impingement or rotator cuff integrity will also assess the strength of the infraspinatus (e.g. the Resisted Isometric External Rotation Test). The previously mentioned study conducted by Reinold and colleagues also evaluated the %MVIC of the infraspinatus musculature during the same exercises. The three most demanding exercises for the infraspinatus included Sidelying External Rotation at 0° of abduction (62% MVIC), Standing External Rotation in the scapular plane (53% MVIC), and Prone External Rotation at 90° of abduction (50% MVIC). Based on the line of pull and perceived action of the infraspinatus, this data seems to make reasonable sense. Additionally, when having your patient perform side-lying external rotation, consider having them place a rolled towel between their arm and their torso. By making this simple adjustment, it is postulated that the muscles controlling adduction and those performing external rotation are more appropriately balanced. The data from these two exercises agree with this theory as %MVIC of the infraspinatus increased from 20% to 25% MVIC with the addition of a rolled towel. When progressing to more functional weight bearing exercises, Uhl et al determined that infraspinatus activity was substantially more active than the other rotator cuff musculature measured. They found the Push-up with feet elevated (52% MVIC) and One-armed Push-up (82% MVIC) to be especially challenging. Obviously, these are more challenging activities and are not appropriate for every patient, but may be beneficial adjunctive exercises for the more advanced clientele.

Teres Minor:

The smaller, but still important, teres minor attaches inferior to the infraspinatus at the lateral border of the scapula and inserts onto the inferior facet of the greater tubercle of the humerus. The teres minor’s primary role is external rotation and stabilization of the humeral head within the glenoid fossa. Secondary actions include adduction and horizontal abduction of the humerus. Teres Minor mm. While, in general, teres minor performs similar actions to the infraspinatus. It provides drastically less activity during flexion, abduction, and scapular abduction than the infraspinatus. It may be isolated with the Dropping Sign Test, which has been shown to have poor sensitivity, but good specificity (Hertel et al).  With regards to exercise prescription, the three most demanding exercises (as determined by Reinold and colleagues) are Sidelying External Rotation at 0° of abduction (67% MVIC), Standing External Rotation in the scapular plane (55% MVIC), and Prone External Rotation at 90° of abduction (48% MVIC). Once again, given this muscle’s line of pull, the data with regards to these exercises make both biomechanical and anatomical sense. Horizontal abduction was also evaluated as it was shown to have substantial activation (74% MVIC) in a previous study conducted by Townsend et al. However, Reinold’s more recent study showed a relatively small contraction of both the infraspinatus (39% MVIC) and teres minor (44% MVIC). As both the infraspinatus and teres minor are the primary external rotators at the glenohumeral joint, it is important to understand which exercisesimultaneously activates both muscles. Reinold has determined the exercises that elicite the highest combined EMG activation are shoulder ER in side-lying, standing ER in the scapular plane at 45° of abduction, and prone ER in 90° of abduction.

Subscapularis:

The subscapularis is the only rotator cuff muscle that is located on the anterior surface of the scapula. With an origin at the subscapular fossa and insertion laterally onto the lesser tubercle of the humerus, its primary action is internal rotation of the humerus. Secondary actions include humeral adduction, production of an abduction torque during arm elevation, glenohumeral compression, and anterior stabilization of the glenohumeral joint. Subscapularis mm. As with the supraspinatus, the subscapularis can produce its maximal force when the humerus is positioned at 0° of abduction. As the abduction angle increases, the moment arms of the inferior and middle heads stay relatively constant.However, the moment arm of the superior head progressively decreases until approximately 60° abduction, which translates into diminished torque production. There have been many studies with conflicting results in terms of optimal abduction angle for subscapularis force production. In place of definitive EMG conclusions, potential for compensation should be taken into consideration. With the arm positioned at 0° of abduction, Decker et al found increased activation of the pectoralis major, latissimus dorsi, and teres major, which indicates a greater potential for substitution and masking of subscapularis weakness. In contrast, it was determined that pectoralis major activity decreased substantially when internal rotation was performed at 90° of abduction.

While this study did not clear up any of the murkiness in regards to subscapularis activation, it did offer assistance in avoiding or detecting compensatory muscular substitution. Decker et al also determined three more complex movements that created substantial subscapularis activity. The Push-up Plus (135.5% MVIC), Diagonal (99.7% MVIC), and Dynamic Hug (94.1% MVIC) exercises all created subscapularis activity that exceeded performance during isolated internal rotation exercises. Although these values are much greater than those reported for isolated internal rotation exercises, the potential for muscular substitution is likely with these more dynamic and functional exercises. Based on these considerations, isolated internal rotation should not be dismissed, but rather used in conjunction with these more demanding activities.

Additional Considerations:

Movement at the glenohumeral joint is complex and dependent on many different muscular actions as well as the contributions of several other joints. While strengthening of the rotator cuff and scapular stabilizers is often directed for patients with shoulder pathology, other regions and joints must also be evaluated. Contributions of the cervical spine, thoracic spine , scapulothoracic joint, acromioclavicular joint , sternoclavicular joint, and passive ligamenous structures can affect the underlying pathology and subsequent rehabilitation process. This is why manual therapy is often directed at these areas. Not only can it increase  mobility, but it can also improve the quality and strength of the exercise (Bang et al).

Additionally, scapulothoracic and pectoral musculature is also necessary for optimal shoulder biomechanics and must be addressed when appropriate. A recent continuing education course taught by Lenny Macrina, MSPT, SCS, CSCS provides a solid evidence-based explanation of the various factors involved in a successful rotator cuff and/or subacromial impingement program (“Glenohumeral Joint Biomechanics and Rehabilitation Implementation”). A comprehensive impairment-based program focused on muscular strengthening, neuromuscular control, endurance, joint hypo/hypermobility, and surgical precautions must be implemented to treat pathologies related to the glenohumeral joint.

Evidence-Based Strength Training: Gluteus Medius

So, there are several pathologies and clinical presentations that may indicate targeting the hip abductors, but are you selecting the most effective interventions?

Lets start off with some anatomy and biomechanics…

The hip abductor musculature consists of the gluteus medius, gluteus minimus, and tensor fasciae latae as determined by Clark et al. Additionally, the piriformis and sartorius muscles work as secondary hip abductors. In addition to being the largest hip abductor muscle, based on its origin and insertion (external surface of the ilium above the anterior gluteal line to the lateral aspect of the greater trochanter), the gluteus medius is also provided with the greatest abductor moment arm. These factors contribute to its place as the dominant abductor muscle and the primary focus of most rehabilitation programs.

Outside of this muscle’s obvious role (hip abduction), it has the additional responsibility of controlling frontal plane stability of the pelvis during walking and other functional activities. During a large portion of stance phase, the hip abductors stabilize the pelvis over a relatively fixed femur (Hurwitz et al). Additionally during the single limb support phase of gait, without adequate hip abductor torque on the stance leg, the pelvis and trunk may drop toward the side of the swinging limb. This hip abductor activation also contributes most of the compressive forces generated between the acetabulum and femoral head. These functions are of utmost importance in normalizing and improving movement quality during functional activities and/or gait. In summary of this muscle’s actions, the gluteus medius concentrically abducts the hip, isometrically stabilizes the pelvis, and eccentrically controls hip adduction and internal rotation.

There are a bounty of different exercises that are said to ‘target’ the hip abductors or primarily the gluteus medius, but where’s the evidence?

Glute Med Freebody Diagram In 2004, Fry et al proposed that 40-60% of maximal voluntary isometric contraction (MVIC) should be considered the threshold for producing adaptive muscular strengthening. Bolgla et al examined the muscular activation of the gluteus medius during 3 weight-bearing (WB) and 3 non-weatbearing (NWB) exercises in healthy, young subjects via electromyography. This study found that the average percentage of MVIC was increased during WB exercises due to the additional external torque required to maintain pelvic stability. This study showed that the WB pelvic drop exercise demonstrated the greatest gluteus medius activation at 52% MVIC. While all, but 2 of the exercises are within the proposed threshold for muscular strengthening, the total number of exercises was minimal and none of the exercises would be considered ‘functional’ in nature. However, Ayotte et al evaluated the electromyographical activity of some of the major hip muscles during 5 unilateral WB exercises. Glueteus medius activity ranged from 52-36% MVIC with the unilateral wall squat garnering the highest muscular activity. As there was not a mean difference amongst the 5 activities, it is suggested that similar gluteus medius activity is required for all activities measured. To build upon these findings, both Boren et al and Philippon et al evaluated the activity of the gluteus medius during more advanced exercises. Boren et al found the most demanding exercises to be 3 different plank variations along with the single-leg squat task. This increased muscular activity may have been secondary to the increased stabilization necessary to properly perform the task and gives credence to the use of these exercises for more advanced patients or those who have progressed near the end of their treatment.

In clinical practice, unstable surfaces are often included to further stress balance and theoretically impose greater demands on the musculature stabilizing the pelvis. Krause et al investigated the alteration in muscular activation when comparing stable to unstable surfaces. While values of percent MVIC did increase with the addition of an unstable surface, these increases did not reach statistical significance and cannot be considered superior to exercises performed on stable surfaces. It should be noted that this study only used one ‘unstable’ surface (Cor-Tex Balance Trainer) and other surfaces may have yielded more beneficial results.

Additionally, you must consider the interaction of other muscles acting with or against the gluteus medius. It has been proposed that individuals who demonstrate excess femoral internal rotation during functional tasks may be relying too heavily on the tensor fasciae latae (TFL) to control their pelvis in the presence of weak or inhibited gluteus medius musculature. The TFL is generally considered a hip internal rotator in addition to its role as an abductor, thus its over utilization has been theorized to cause abnormal pelvic control. Powers et al conducted a study comparing the %MVIC of the gluteus medius versus that of the TFL in 11 different therapeutic exercises utilizing indwelling fine-wire electrodes. They ranked the exercises based on their calculation of the Gluteal-TFL Activation Ratio. The authors concluded, exercises that produced significant activation of the gluteus medius while minimazing TFL activity included the clam, side-step, unilateral bridge, and hip extension in quadruped on elbows with knee extended or flexed. It must be understood that in general, these comparisons of MVIC have their limitations. Not all the testing procedures were consistent between studies and all subjects measured were young and asymptomatic, which does not necessarily correlate with patients seen in a rehabilitation setting. Also, several studies utilized surface EMG electrodes, which are notorious for crosstalk being recorded from adjacent muscles.

While measurement of MVIC and its application to exercise selection is very beneficial, it should not be your only means of determining proper prescription. You must take into consideration your patient’s current stage in the rehablitation process, potential contraindications, and where your patient’s deficits actually lay. Your patient may have a 5/5 grade on his side-lying hip abductor manual muscle test (MMT), but he demonstrates an inability to control hip adduction and internal rotation during your running and/or gait analysis. The evidence says gluteus medius activity during side-lying hip abduction is 62% when averaged across three studies, pretty good right? Would this be an appropriate exercise for this patient? Probably not. He has no problem with NWB concentric activation of his gluteus medius, but loses isometric and eccentric pelvic control during demanding functional activities. You must select exercises appropriate for your patient, do not get blinded by the statistics, they do not tell the whole story. Use MVIC data to determine which exercises among those appropriate for your patient are most effective. This approach will give you a foundation to stand on when determining your patient’s exercise prescription.

Below is a summary chart of the Gluteus Medius %MVIC data compiled from all the studies referenced in this article.

%MVIC of Gluteus Medius