“. . . according to the Yoga Sutra (3.1), the term [Bandha] refers to the ‘binding’ of consciousness to a particular object or locus (desha), which is the very essence of concentration.”
Georg Feuerstein



Sunday, June 4, 2017

Around Your Core in 4 Minutes

Figure 1: The "Around Your Core" sequence.
Hello Friends,

I want to share one of my favorite core workouts. I use this at the end of practice to integrate the shoulders, core and lower extremities. Let’s get right into it…

1) Start with forearm plank. Tighten your glutes and abs as you attempt to drag your forearms towards your feet. This is an isometric contraction of the core muscles shown below. At the same time, co-activate the muscles of your rotator cuff by attempting to “windshield wiper” your forearms in while resisting this action in the opposite direction (Figure 2). Hold for 10-30 seconds the come down and rest for 10 seconds. Click here to learn the key cues to activate your pose as well as the muscle subsystems it amplifies…

Figure 2: Forearm plank. Attempt to drag your forearms towards your feet.

2) Now go to plank pose on your right side. Press the edge of your right foot into the mat and lift your pelvis. Attempt to drag your forearm towards your foot. Co-activate the rotator cuff by attempting to “windshield wiper” your forearm in internal rotation while resisting with external rotation (Figure 3). Hold for 10-30 seconds the come down and rest for 10 seconds. Click here to learn the key cues to activate your pose as well as the muscle subsystems it amplifies…

Figure 3: Side plank. Attempt to drag your forearm toward your foot and your foot toward your forearm.

3) Next, go to Bridge Pose (Setu bandha Sarvangasana). Engage the muscles that surround your pelvis (including the glute max and internal rotators) and connect them to your back muscles. Hold for 10-30 seconds the come down and rest for 10 seconds. Click here to learn the key cues to activate your pose as well as the progression for contracting the correct individual muscles—this is key!

Figure 4: Bridge pose. Engage your glutes.


Added Bonus: engage the muscles on the sides of your lower legs to lift your feet arches. Click here to learn more about this important cue.

Figure 5: Engage the muscles on the sides of the lower leg to lift your arch.


4) Next roll over to left side forearm plank. Hold for 10-30 seconds then come down and rest for 10 seconds.

5) Return to forearm plank and repeat the sequence, this time starting with left side plank pose.




Keep your breathing smooth throughout this sequence. Be sure to check out the details in the links above. Start with 10-30 seconds in each pose and build to 1-2 minutes. The adjustments in the links are the keys to integrating the extremities and core. For more cues to help you get the most from your practice, page through the Yoga Mat Companion Series and the Key Muscles and Poses of Yoga.


All the Best,

Ray Long, MD

Saturday, May 20, 2017

Your Glutes in Backbends: Part I

Hello Friends,

In this post we take a look at the glute max in backbends and how to avoid splaying out your knees in poses like Urdhva danurasana (Wheel). I give you some cues for sequencing muscle engagement and also address a misconception about contracting your adductor muscles.

For decades now we’ve heard the instruction in yoga, “soften your glutes in backbends” with no valid explanation why. Your hips are extending in backbends, and your gluteus maximus is the prime mover for that action. Why wouldn’t you want to contract the very muscle that creates that movement?

Let's look closer. When you deliberately soften your glutes, then the hip extension comes from the hamstrings, because your hamstrings work as synergists to the gluteus maximus for this action. So, why not just use your hamstrings to extend the hips and avoid getting scolded for using the prime movers (glutes)? Well, if you do that enough, you potentially set up a muscle imbalance that can lead to “synergistic dominance” wherein the hamstrings become the prime mover of this action. In the hip joint, this can result in abnormal kinematics and, ultimately, pain. I’ll go over some other problems with doing backbends without the glutes in Part II of this series.

One side effect of using your gluteus maximus is that it is also a powerful external rotator of the hip. Thus, when you engage your glute max in a backbend, your hips will rotate outward and your knees tend to splay apart.

Do we care if the knees splay out? Well, it depends on your objective in the pose. Recent literature shows that if the femurs are parallel, you fire your entire gluteus maximus, whereas when they are splayed apart, you fire mainly the upper portion (Selkowitz, 2016).

The “solution” that is usually proposed for this is to have folks try to squeeze a block between their knees to “fire those adductors!” In India, this instruction was often accompanied by much shouting at the frustrated person attempting it. There is a reason, however, why this cue works so poorly, despite the yelling. That is because when your hips are extended (in a backbend), the orientation of the adductor muscle fibers makes them become external rotators of the hip and synergize the gluteus maximus in splaying your knees apart. So it’s a bit like hitting the brakes and gas at the same time. Frustrating. Figure 1 illustrates this.

Figure 1: Note the orientation of the fibers of the adductor group and how contracting these muscles leads to splaying out of the knees in backbends.

The real counterbalance for the gluteus maximus causing the knees to splay apart is to contract the muscles that internally rotate the hips, namely, the TFL and front part of the gluteus medius.

This cue works well, but it must be implemented in a sequence to function optimally. You have to engage the hip internal rotators before going up into the backbend. It's difficult to engage them once you are up in the pose because when the hips are extending, the TFL and front part of the gluteus medius are at a biomechanical disadvantage for initiating contraction. Thus, you want to first train the cue to engage these muscles with the hips flexed, where it is easy to contract them. Then bring in the glute max to do the backbend. I’ve taught this sequence all over the world and had great feedback. Done properly, the muscles form a “sheath” that lifts the pelvis in a balanced and stable fashion. (Figure 2)

Figure 2: Note how the muscles at the front of the hips internally rotate the thighs to balance external rotation from the gluteus maximus.

Here’s the sequence.

Step 1) 

Lie on your back and bend your knees so that your feet are flat on the ground as shown. Place your hands on the front part of the pelvis to feel your internal rotators contract. Now, on exhalation, press the feet down and attempt to scrub them apart while allowing you knees to roll inward. Don’t actually move your feet. You should be able to feel your TFL contract. Release on the inhalation and repeat for about 10 times to train the action. Press your feet down and then attempt to scrub them away from the midline. The feet should remain fixed on your mat, as your knees roll inward and you should feel your muscles contract if you've got it.

Figure 3: Press your feet down and attempt to drag them apart as you allow your knees to roll inward. Place your hands on the front of your hips to feel the TFL and front of the gluteus medius contract with this action.

Step 2)

Follow the instruction from step 1, maintain the cue of pushing away from the midline with your feet and then dial in contraction of the gluteus maximus to lift the pelvis. You will be pushing down and away from the midline to engage your internal rotators and then engaging your glute max to extend the hips. Go up on the exhalation and down on inhalation. Try this about 10 times (2-3 sets). I recommend working with this set of cues for a few days before integrating them into a full back bend. Once you get it, then try the block thing (if you want). You’ll find it works better this way.

(NB: if you experience knee pain in this pose, try pressing down with the heels more--this often helps.)

Figure 4: This illustrates the sheath of muscle surrounding the pelvis and lifting it into the bridge.


I hope you enjoy this post. Use muscle engagement as a barometer to help identify imbalances between the two sides of the body. Then carefully work to balance things. This is one of the benefits of practicing Hatha Yoga using knowledge of anatomy and biomechanics.

Good to see you all again. Check back for Part II in the sequence when I will go over the role of the deep external rotators and discuss synergistic dominance of the hamstrings in more detail.

All the Best,

Ray Long, MD

References:

1) Selkowitz, D. M., Beneck, G. J., & Powers, C. M. (2016). Comparison of Electromyographic Activity of the Superior and Inferior Portions of the Gluteus Maximus Muscle During Common Therapeutic Exercises. Journal of Orthopaedic & Sports Physical Therapy, 46(9), 794-799. doi:10.2519/jospt.2016.6493


Thursday, April 7, 2016

Your Glutes and Lats in Bird Dog Pose

Hello Friends,

Once you learn the individual muscles, then it’s time to look at how they function together during movement and in your asanas. Use your knowledge to develop cues to refine and deepen your poses. Groups of muscles, ligaments and fascia that function together are known as “subsystems”. In this post we examine the posterior oblique subsystem in Bird Dog pose.

The posterior oblique subsystem is comprised of the gluteus maximus on one side of the body and the latissimus dorsi on the other side, with the thoracolumbar fascia between (as shown in the inset illustration). These structures operate synergistically with other groups of muscles, ligaments and fascia, particularly during rotational movements such as a golf swing. 

Figure 1 illustrates how the fibers of the gluteus maximus and opposite side latissimus dorsi run perpendicular to the sacroiliac joint. Co-contracting these two muscles can be used to tension the thoracolumbar fascia, thus stabilizing the sacroiliac joint. Click here to learn more about the thoracolumbar fascia and its important role in core stability.

Bird Dog is an excellent pose for strengthening the core and engaging the posterior oblique subsystem. A good cue for activating the latissimus dorsi muscle in this pose is to straighten the arm forward and then imagine pushing down with the hand against an immoveable object (as shown with the dotted arrow). Alternatively, imagine pulling down on a rope with the forward hand. Combine this isometric contraction of the lats with engaging the gluts on the side of the lifted leg to augment the stabilizing effect on the SI joint.



Figure 1: The posterior oblique subsystem and sacroiliac joint in Bird Dog Pose.


Click here to check our our previous post, "Connect Your Cuff to Your Core in Forearm Plank" and see how this subsystem works in plank pose. With this in mind, what other poses can be used to activate the posterior oblique myofascial subsystem? Place your answer in the comment section below…

Thanks for stopping by--I hope you're enjoying learning about biomechanical concepts like the myofascial subsystems and how they work in your poses. Stay tuned for the next post when I'll go over the hamstring connection to the pelvis and lumbar. Click here to browse through the Bandha Yoga book series on anatomy, biomechanics and physiology for yoga.


All the Best,


Ray Long, MD

Tuesday, April 5, 2016

Connect Your Cuff to Your Core in Forearm Plank

Update on Forearm Plank: 

One of my goals in reviewing the scientific literature is to identify information that can be translated into a practical cues that you can integrate into your practice. With this in mind, I want to call your attention to a new study from the Journal of Strength and Conditioning Research

The investigators showed that drawing the shoulder blades (scapulae) towards the midline (adducting) and tilting the pelvis back and down (retroverting) resulted in greater activation of the rectus abdominis, external oblique, internal oblique and erector spinae muscles. 

Figure 1 shows you the muscles involved in this cue. Engage your rhomboids and middle trapezius to draw your shoulder blades towards the midline. At the same time, engage your glutes and rectus abdominis to retrovert the pelvis. Take a look below at how this fits in with the other cues for forearm plank that I describe below on connecting your cuff to your core!

Figure 1: Adducting the shoulder blades and tilting the pelvis helps to activate your core.

Your wrists are not an area where you want to “work through pain”...

Scientific studies have demonstrated that having a strong core can improve the efficiency of your rotator cuff. A strong and efficient rotator cuff leads to improved stability of your shoulder girdle. This decreases load transfer to your wrists in poses where you bear weight on the hands (like arm balances, Dog Pose and Chaturanga).

Conversely, if your core is weak, or you don’t properly engage it in these types of poses, your cuff is less efficient and your wrists have to bear more of the load. Practicing with imbalances of this nature can lead to a cycle that reinforces the imbalance and, ultimately, injury to the wrist (and shoulders).

The Sanskrit term “Ahimsa” means nonviolence or reducing harm (translation from Nicolai Bachman’s book “The Language of Yoga”). While this term is often used in relation to social ethics, it also applies to how we work with the body.

Reducing the risk of harm to your wrists (and other joints) can include decreasing the frequency and duration of poses that load the wrists and correcting imbalances in the postures. If you have developed wrist pain, you should consult a trained medical professional and work under their guidance. Managing wrist pain almost always includes a period of time off and resting from weight bearing poses, usually combined with some light wrist mobility exercises.

In the interim, I’ve found that Hard Style Plank Pose is a great pose to work on. That’s because it’s awesome for strengthening the core and addressing the underlying imbalance and it doesn’t involve weight bearing on the wrist. Figure 1 illustrates this pose.



Figure 2: Forearm Plank Pose with the posterior oblique myofascial subsystem.

In Hard Style Plank, your weight is on your forearms, with the upper arm bones (the humerus) perpendicular to the floor (in Chaturanga, they are parallel to the floor). Clench your fists to strengthen the muscles that cross the wrists. Then press your forearms into the mat and gently attempt to internally rotate the shoulders. Your forearms are fixed on the mat and don’t actually move. Next, co-contract the external rotators of your shoulders by attempting to externally rotate them. The cue for this is to pretend that your forearms are like windshield wipers that are fixed in place. This co-contracts the subscapularis, infraspinatus and teres minor muscles of the cuff and connects them to your core. Finally, engage the lats and attempt to drag the forearms towards the feet while, at the same time, contracting your abs and gluts. Hold for five to ten seconds and repeat two times. Remember to breathe!

Figure 1 above illustrates the muscles involved here, with color-coding according to the strength of your engagement. Check out the posterior oblique subsystem of the lats, thoraco-lumbar fascia and gluts. Engaging this connection helps stabilize the SI joint. Click here for info and illustrations of side forearm plank and the another myofascial subsystem. Click here and here for more on the gluts and abs connection and the lumbar spine in Chaturanga.


As an aside, soaking your wrists in ice water between sessions of injuring them is a lousy solution; it doesn’t address the underlying imbalances and can lead to more injury. You have to dedicate time off from weight bearing to let your wrists heal, not to the “practice” of injuring them.

Thanks for stopping by--I hope you're enjoying learning about biomechanical concepts like the force couple. Stay tuned for the next post when I'll go over the hamstring connection to the pelvis and lumbar. Click here to browse through the Bandha Yoga book series on anatomy, biomechanics and physiology for yoga.


All the Best,


Ray Long, MD



Saturday, March 19, 2016

Shoulder Biomechanics, Part III: The Supraspinatus Muscle

Hello Friends,

Let’s cap off the muscles of your rotator cuff with the supraspinatus. This muscle originates in a trough-like area above the scapular spine, hence its name supra, which means “above”. The supraspinatus then inserts onto the greater tuberosity just behind where the long head of the biceps enters the shoulder (figure 1).

(We’ve covered the subscapularis, infraspinatus and teres minor muscles along with some key biomechanical points about each muscle—click to review.)




Figure 1: The supraspinatus muscle of the rotator cuff (with the infraspinatus and teres minor faded).


Contracting the supraspinatus abducts the humerus at the glenoid socket (takes the arm out to the side) for the first 15 degrees. After that, it becomes a synergist of the deltoid for abduction. As with the other muscles of the cuff, the supraspinatus also stabilizes the humeral head in the socket. Figure 2 illustrates this in Warrior II. 


Figure 2: The supraspinatus contracting to synergize the deltoid in abducting the shoulders in Warrior II.


The supraspinatus is the rotator cuff muscle that is most frequently torn. Tears start to become common beyond the age of forty, with an increased incidence in each decade of life. Figure 3 illustrates a supraspinatus rotator cuff tear.



Figure 3: Full thickness tear of the supraspinatus muscle (with the long head of the biceps shown in front of the supraspinatus).


Drawing your arm across the chest (adducting it) stretches the supraspinatus, as well as the capsule of the shoulder and the deltoid muscle. Figure 4 illustrates this action in Garudasana. Note the muscles (colored blue) that contract to stretch the supraspinatus and the muscles that also stretch in this pose (colored red). 


Figure 4: The supraspinatus muscle stretching in Garudasana. The muscles in red are stretching and those in blue are contracting.


Click here to take the rotator cuff quiz to test your knowledge!

Thanks for stopping by. Stay tuned for the next post when I'll go over the interaction between the deltoid muscle and the rotator cuff. By the end of this four-post series, you'll have a good understanding of the functional anatomy and biomechanics of the shoulder joint as applied to yoga. Click here to browse through the Bandha Yoga book series on anatomy, biomechanics and physiology for yoga.


All the Best,


Ray Long, MD

Sunday, March 13, 2016

Shoulder Biomechanics, Part II: The Infraspinatus & Teres Minor Muscles


Hello Friends,

Welcome to the second of the four-part series on the shoulder joint. Last week I discussed the subscapularis muscle, which is the main shoulder internal rotator. Now we’re on to the antagonist muscles of the subscap, namely, the infraspinatus and teres minor. The infraspinatus arises in a trough below the scapular spine, hence its name (“infra” means below). The teres minor arises back part (dorsum) of the scapula along its outer (lateral) border. The infraspinatus and teres minor insert onto the back part of the greater tuberosity of the humerus, as shown in Figure 1. 

These muscles externally rotate the humerus, with the infraspinatus being the strongest external rotator of the joint. The infraspinatus and teres minor also function to stabilize the humeral head in the socket (glenoid).




Figure 1: The infraspinatus and teres minor muscles of the rotator cuff (the supraspinatus is the faded muscle on top).


The Force Couple

These muscles combine with the subscapularis at the front of the joint to form a “force couple”. In this manner, antagonist muscles (for rotation) become synergists (for stability). Therapy (and surgery) for rotator cuff pathology is directed towards restoring this force couple. Click here to read about concept of antagonist/ synergist combinations for the hip muscles in yoga. Click here for some cues to use this in Dandasana.
Figure 2 illustrates this biomechanical process. This view is looking down on the shoulder with the front of the joint towards the bottom of the page



Figure 2: The force couple between the infraspinatus and subscapularis muscles. This view is looking down on the shoulder with the front of the joint towards the bottom of the page.

Poses with the arms in reverse Namaste' stretch the infraspinatus and teres minor, as does Gomukhasana. Those of you who are more flexible may gently press the knife edge of the hand into the back to "load" the external rotators. Folks who are tighter may simply grasp the elbows or hands behind the back. Click here for more details and an animation of Gomukhasana stretching these muscles as well as a not so obvious cue for loading and using PNF for this stretch.

Figure 3: Stretching the infraspinatus and teres minor by internally rotating the shoulders in Parsvottanasana.


Externally rotating the shoulders in poses like Trikonasana (Triangle) can be used to activate the infraspinatus and teres minor. Figure 4 illustrates this, as well as the myofascial connection between these muscles and the muscles that retract the scapula, namely the trapezius and rhomboids.




Click here to take the rotator cuff quiz and test your knowledge!

Thanks for stopping by--I hope you're enjoying learning about biomechanical concepts like the force couple. Stay tuned for the next post when I'll go over the last muscle of the rotator cuff, the supraspinatus. Then I'll finish up with the relationship between the rotator cuff and the deltoids. By the end of this four-post series, you'll have a good understanding of the functional anatomy and biomechanics of the shoulder joint as applied to yoga. Click here to browse through the Bandha Yoga book series on anatomy, biomechanics and physiology for yoga.


All the Best,

Ray Long, MD

Sunday, March 6, 2016

Shoulder Biomechanics, Part I: The Subscapularis Muscle

Hello Friends,

This is the first of a four-part series on the shoulder joint, focusing specifically on the rotator cuff and its biomechanical relationship with the deltoid muscle. Let's begin by looking at the muscles that comprise the rotator cuff, starting with the subscapularis. As figure 1 illustrates, the subscapularis occupies the space, or fossa, at the front of the scapula. From there it attaches to the lesser tuberosity, a knob-like structure on the humerus bone at the front of the shoulder. Concentrically contracting the subscapularis muscle (shortening the muscle on contraction) internally rotates the shoulder. The subscap also acts, in conjunction with the infraspinatus muscle, as a stabilizer of the humeral head in the socket (glenoid). We test strength and function of this muscle with the "belly press" test or the "bear hug" test. Tightness in the subscapularis can limit external rotation of the shoulder.


Figure 1: The subscapularis muscle, illustrating the origin on the inside of the scapula and the insertion on the lesser tuberosity of the humerus.


Figure 2 illustrates one of the poses that stretch the subscapularis muscle, namely, Gomukhasana. The upper side humerus externally rotates in this pose, thus stretching the muscle as shown.

Figure 2: This illustrates the effect on the subscapularis muscle of the upper arm in Gomukhasana. External rotation of the humerus stretches the muscle.


Figure 3 illustrates engaging the subscapularis muscle in Ardha Baddha Padma paschimottanasana. Advanced practitioners can attempt to lift the hand off the back to engage the muscle in this pose. This also replicates the "lift off" test, which is used in orthopedics to test the function of the subscap muscle.

Figure 3: This image illustrates contraction of the subscapularis muscle to internally rotate the humerus.



Finally, we have the subscapularis as a stabilizer during a static position in a pose. In Warrior II, attempt to internally rotate the shoulders by imagining pressing the mound at the base of the index fingers down against an object. Resist this by externally rotating the shoulders at the same time. Co-contracting opposing muscles--like the subscap and infraspinatus--stabilizes the head of the humerus in the socket while the deltoid contracts to abduct the humerus. Click here to go into a bit more depth on the subject of stabilizing your shoulders in your Downward dog pose. 


Figure 4: Co-contracting the subscapularis and the infraspinatus stabilizes the humeral head in the socket while the deltoid muscle abducts the humerus.



Click here to take the rotator cuff quiz and test your knowledge!

Thanks for stopping by. Stay tuned for the next post when I'll go over the antagonist muscle for the subscapularis. By the end of this four-post series, you'll have a good understanding of the functional anatomy and biomechanics of the shoulder joint as applied to yoga. Click here to browse through the Bandha Yoga book series on anatomy, biomechanics and physiology for yoga.

All the Best!

Ray Long, MD

Friday, November 6, 2015

Stabilizing Your Shoulders In Downward Dog

Hi Folks,

In our last post, we discussed joint rhythm for the shoulders. In this blog post I want to share some of my recent investigations on the biomechanics of the shoulder joint, with some specific tips for Down Dog. Shoulder pain is one of the problems that comes up in yoga, especially with folks who are doing Vinyasa based practice. The underlying cause of the pain can be multifactorial, but it is frequently related to impingement of the rotator cuff and subsequent inflammation of the cuff tendon (specifically the supraspinatus muscle). Inflammation of the tendon, in turn, affects function of the shoulder. Weakness or instability in the shoulder can then lead to abnormal pressures at the wrist, causing pain there as well. Thus, stabilizing the shoulders has beneficial effects beyond the shoulders. is a complex process involving strengthening the core and then linking the strong core to the shoulders.

With this in mind, let’s look at one of the key factors in shoulder impingement, namely, the acromio-humeral interval. This refers to the distance between the undersurface of the acromion and the humeral head, as measured using radiology intruments (x-ray, ultrasound, mri). The acromion is a shelf of bone on the scapula, above the spine (seen in Figure 1). It serves as the attachment for the deltoid muscle. The humeral head articulates with the shoulder joint and serves as the attachment for the muscles of the rotator cuff (on the greater and lesser tuberosities). Factors that decrease the space between the acromion and humeral head can lead to inflammation of the cuff tendon due to compression between the two bones.

Figure 1: The acromio-humeral interval. 

Research has shown that contracting the main adductor muscles of the shoulder serves to increase the acromio-humeral distance. These include the pectoralis major and latissimus dorsi. Co-contracting the biceps and triceps muscles when the arms are overhead can also draw the humerus away from the glenoid, as shown in Figure 2. Finally, externally rotating the shoulder humerus moves the vulnerable area of the supraspinatus tendon away from the area where it would impinge on the acromion (click here to learn more).

Figure 2: The long head of the triceps and short head of the biceps in relation to the gleno-humeral joint with the arms overhead.

Here’s the cue…

Warm up first a bit. Then, take Downward Dog pose. I use three steps for the shoulders. Go slowly and use gentle engagements.

  1. Contract the triceps to straighten your elbows. Then, press the mound at the base of your index fingers into your mat to engage the forearm pronator muscles.
  2. Next, fix your palms into the mat and try to drag the hands towards each other. This engages the adductor muscles of the shoulders as well as the biceps.
  3. Finally, gently roll the shoulders outward. This externally rotates the humerus bone and helps to bring the greater tuberosity away from the undersurface of the acromion.

Figure 3 illustrates the various muscles involved in these cues.

Figure 3: Attempt to drag the hands towards one another. This engages the shoulder adductors. Then externally rotate the shoulders.

As a final adjustment, I like to link the action of the shoulders to the lower extremities. The cue for this is to engage your lower gluteus max and adductor magnus muscles by drawing in with the upper inner thighs and then attempt to drag your feet away from the hands. Feel how this stabilizes your pose. See Figure 4 for the graphics.

Figure 4: Engage the lower parts of the gluteus maximus and adductor magnus as you attempt to drag the feet away from the hands to stabilize the pose.

Bear in mind that shoulder stability is a complex process. The shoulders are linked to the core; so building a strong core leads to stable shoulders. Stable shoulders help to protect the wrists, and so on. Click here to read more on your core. If you would like to learn more anatomic sequencing to improve your poses, click here to take a tour of The Yoga Mat Companion Series.

Thanks for stopping by—see you in a couple of weeks for another post on combining anatomy, biomechanics and yoga.

All the Best,

Ray Long, MD



References:


  1. Graichen H1, Bonel H, Stammberger T, Englmeier KH, Reiser M, Eckstein F. Subacromial space width changes during abduction and rotation--a 3-D MR imaging study. Surg Radiol Anat. 1999;21(1):59-64.
  2. Hinterwimmer S1, Von Eisenhart-Rothe R, Siebert M, Putz R, Eckstein F, Vogl T, Graichen H. Influence of adducting and abducting muscle forces on the subacromial space width. Med Sci Sports Exerc. 2003 Dec;35(12):2055-9.