How To Screen Your Low Back Pain

There is always a reason for back pain. It doesn’t just appear out of thin air and it’s not “all in your head.” In order to fix and remove the pain, we need to find out why it started in the first place.

In my career as a physical therapist, I have spent countless hours reading, researching, and implementing many methods and techniques from experts across the world that have come before me. I did not invent the following screens and tests that I’m sharing with you today. Instead you will find they are a combination and blending of the ideas and teachings from experts I myself have learned from (including but not limited to Dr. Stuart McGill and Shirley Sahrmann) and molded into my own approach of evaluating patients. It is only due to the wisdom that these experts have shared with the world that I am able to sit here today and write to you.

Most injuries that occur in the weight room are due to poor movement and technique when lifting. Over time poor technique creates tiny amounts of trauma to your body that eventually cumulate and lead your body over the proverbial ‘tipping point’ into injury. The framework for the theory that flawed mechanics or movement leads to pain has been called the kinesiopathologic model or KPM.^2,5While the model has a pretty fancy name that most of you will never have to remember, the idea behind it is key to fixing your pain: start by finding out what movement problems led to the injury developing in the first place.² Pretty simple.

The reason this model is so different than the way in which many in the traditional medical field have treated back pain is that it attempts to treat the cause or why behind your pain (poor movement) rather than focus on trying to “treat” the specific tissue or part of your spine that may be injured (disc bulge, arthritic facet joint, fractured end plate of a vertebrae, etc.)² Basically, the goal is to take a giant step back and view how the body moves from head to toe rather than look at the injury through a microscope or with an MRI. By stepping back, you avoid tunnel vision with low back injuries. Treat the person, not the injury.

Here’s a brief example of this concept at work. Jerry is a 24-year-old powerlifter who was referred to physical therapy with a diagnosis that reads “Low back pain due to disc herniation at L4/5.” The disc herniation would be the specific anatomical cause of pain that his orthopedic doctor would like to fix. Through the examination I found that he had poor core stability and an inability to squat deep or perform a deadlift without his back excessively rounding. Any time he rounded his back in this manner he had extreme low back pain.

Screening and classifying someone in pain based on the movement problems that cause pain (an inability to tolerate bending of the spine or “flexion intolerance” along with poor core instability) is more useful to driving the treatment process of the injury than knowing the exact anatomical cause of pain (disc herniation). Knowing someone has a disc herniation doesn’t necessarily tell me why he or she has pain or what needs to be corrected. Also, as we have disused in detail before, it is very common to find ‘abnormal findings’ such as a disc bulge through traditional imaging (MRI) in people who are completely pain free! For example, research that looked at the backs of pain-free 20-year-olds and found nearly 30% to have a disc bulge!¹⁶

Therefore in order to give Jerry a diagnosis that will categorize the type of pain he is having and serve as a catalyst to drive the kind of treatment his individual body needs to recover I would classify his injury as “low back pain due to flexion intolerance and core instability.”

During the screening process we’ll go over next, I want you to think about which of the following categories your back pain fits the most. Gather clues from each screen and test to help you figure out what type of posture, movement or load is the why behind your back pain.

• Flexion Intolerance
• Extension Intolerance
• Rotation with Extension Intolerance
• Load Intolerance

Step 1

The first step in screening your low back is to do an in depth self-analysis of what triggers your pain. We need to find out exactly what causes your pain. These are the activities, movements and postures you assume throughout your day that bring out your symptoms. Think hard and write down your answers on a sheet of paper, as the answer is rarely “everything you do.” Here are a few examples and things to keep in mind as you compile your list.

As strength athletes, excessive movement of the low back in training and on the competition stage are often huge predictors of the type of back pain we will experience. Think about all of the repetitive lifts or movements you do in the gym that create pain (either during or after). Once you’ve placed your finger on the one or two things that lead to pain, can you find a common movement or posture your back is in during them? For example, the CrossFitter who feels back pain after performing 300 bodyweight air squats in a WOD with excessive butt wink can link excessive flexion or bending motion of their spine during squats as a possible trigger of pain.

Along with your assessment of the movements in the gym that trigger your pain, the postures you assume and movements you put your body through during the other 22-23 hours of the day outside of training are just as important to evaluate. The accumulated micro-trauma that caused your current back pain may not be solely due to training.

Think to yourself whether or not rounded or extended postures (such as sitting for an extended period or walking and standing) create or alleviate pain in your back. For example, I have many patients who complain of back pain after sitting all day at work yet have none if they are up and walking. However, some people may have pain when walking/running for 15 minutes but is relieved with sitting or forward bending.³ Do either of those situations sound familiar?

Another example of a possible trigger would be load related pain. An athlete who experiences pain only when lifting over 70% of their 1RM is experiencing symptoms that are directly related to the amount of compression or shear forces acting on the spine due to the weight on the barbell. If this sounds familiar, write down not only the amount of weight you start to experience your symptoms but also analyze the motion and postures you are assuming during that specific exercise.

After doing your self-assessment, did you find a common motion, posture or load that triggers your pain? Did you also notice any specific movements that you can do without pain? If you did, you should breathe a sigh of relief. You just took the first step in eliminating your pain by making a conscious connection and link to the cause of your pain.

Step 2

To help give us an even better idea to the cause of your pain, we will now perform a few tests. Again the goal is to identify postures, motions and loads that trigger your pain and those that can be performed without.² By pinpointing these problematic factors and making the invisible now visible, we can then work to decrease your symptoms and return to lifting pain free.

Standing Assessment

One of the first things I do as a physical therapist during the assessment of a patient with low back pain is to watch how an athlete stands and moves. As the great Yankee Yogi Berra once said in one of his witty sayings, “You can observe a lot by watching.”

Start by standing in your normal posture as if you’re waiting in line at a grocery store. Have a friend take a photo of you from the side, front and from the back. What do you notice about your standing posture? Are your shoulders rounded? Is your chin poking out in front of your body? Is your low back flat or does it have an excessive arch? Do you feel certain muscles of your back flexing or contracting hard?

Poor posture causes certain muscles of our body to remain “on” and active during the day. Many people who develop back pain assume postures that don’t allow their low back muscles to relax.

If this is you, try to change your posture right now by using the cue to “stand tall” or “stand like a military officer” and see how that affects your low back stiffness. Brace your core slightly, squeeze your glutes and try to stand with “perfect posture.” Did anything change? The goal is to teach your body a new way to stand that is pain free and alleviates tension in your body. If changing the way you stand already modified your pain levels, you have found a way to modify and wind-down your symptoms!

Next, perform a deep bodyweight squat and hold the bottom position. Have a friend watch and observe what happens to your low back as you reach the deepest portion of the squat.

Often those who have pain while sitting in the bottom position of a squat do so because they have a posterior pelvic tilt (butt wink) that created an excessive round in the low back.  During the descent of the squat the thigh bone (femur) rotates in the hip socket (called the acetabulum). As the depth of the squat increases, the femur can eventually come into contact with the front rim of the socket. The timing of this contact will depend on the size of the femur and the depth of the socket (something we can thank our parents for). Because the femur can no longer rotate at this point, the pelvis must reflexively rotate backwards in order to continue the descent of the squat which then brings the low back into a rounded position as well.

Is having butt wink automatically a sign of impending back pain? Not necessarily. However, if the motion happens to a great degree under load and/or occurs enough times during the squat, the potential to create a back injury greatly increases.

If this motion creates pain during the screening of the squat, you likely have a flexion intolerance problem. The presence of pain in this deep squat with a rounded back is clueing you that the position of your pelvis when lifting is a factor in creating your symptoms. Your first step is to be cognizant of how much butt wink your body has when squatting or dropping under a clean or snatch. The second step should be to also check out the mobility of your ankles.

Why does ankle mobility matter when it comes to low back pain? When the ankle becomes stiff and immobile (particularly in the movement of dorsiflexion) the knee will be unable to push forward over the toes during the deepest portion of the squat. This means if you continue to descend into a deep squat, another part of your body (the pelvis and low back) has to give way and move excessively.^10-12

If you haven’t tried it yet, the 5 inch wall test is an easy way to screen for ankle mobility problems. If this screen was able to uncover a significant restriction at this joint, working everyday to improve this mobility should be a priority if you wish to return to deep squatting pain free!

Next, pick up an unloaded barbell and hold it at your waist in the hang position. Let the barbell drop down to the middle of your shins as if you are performing an RDL (Romanian Deadlift). If you don’t have a barbell, just mimic the motion by having your hands by your side.

Hold this for a few seconds and then return to the start position. What did you experience? If you had pain during the motion of bending forward, it’s means again you have a flexion problem. If however you didn’t have pain while bending over, however had pain during the return movement it’s a sign of having an extension issue. Athletes who have pain upon returning from this forward position frequently move from their low back first and THEN the hips (lumbar extension followed by hip extension).

If you had pain during this test due to either reason, try to correct for your low back position by holding it in neutral by bracing your core and properly hinge from the hips. Don’t let your low back arch or round as you go down and squeeze your glutes while driving your heels into the ground on the ascent.

Did you find a slight decrease in pain compared to the first time? If so, you need to learn how to properly hinge at the hips and limit excessive movement (either in flexion or extension) from your back!

Sitting Assessment

One of the simplest screens to assess how your body responds to certain postures while lifting is to use a seated compressive test. This is a test I picked up from Dr. Stuart McGill, and have found it to be very helpful in the evaluation process with my patients.

Start by sitting on a stool with your arms by your side. Assume a good postured “tall” position with your spine in neutral (there will be a small arch in your low back).

Next, grab the stool with your hands and pull upwards to compress your spine. What did you feel? Did this action create pain in your back? Next, round your lower back and perform the same pulling motion. What happened this time? Did you have pain in your back now that it we added a bit of compression in the rounded position? Do the test one more time, but now with an overly arched back (spinal extension). Write down what you find.

If you found pain presented when sitting with good posture during this screen, we can conclude that your symptoms are due to compression. Even when lifting with good posture, the added compression at this time (that largely comes from muscle contraction) is too much for your back and you must stop lifting heavy for the time being if you want your back to heal.

If instead you had pain that presented when rounding your back or extending your back under compression we can assume your back injury is triggered by postures out of “neutral.” We can refer to these problems as a “flexion intolerance” if your pain was brought out when rounding your back during the screen or “extension intolerance” if it was with the overly arched back.

Prone Assessment

Next, find a bed or a spot on the floor and lie flat on your stomach. If this starts to hurt, stand back up and move to the next assessment (you likely have an extension intolerance that makes lying flat on your stomach painful). If this position is pain free, remain lying on your stomach for a few minutes. After, stand back up without letting your spine round (push up from your hands).

Did you notice anything different? If your pain is reduced after lying on your stomach for a few minutes we can assume that your back pain is in part triggered when in a flexed or rounded spine posture because we are able to unload it and make it feel better when putting it in a slightly extended position during this test.

In that same prone position (lying on your stomach), raise one leg at a time off the table (make sure to keep it completely straight). It doesn’t need to move far but each of us should have around 10 degrees of hip extension. Assess both legs and compare how much movement occurs at each hip and whether or not any pain was produced in the low back.

If pain was produced by extended your leg off the bed (the movement of hip extension) place a pillow under your stomach. Try the same test again, but this time brace your core muscles like you’re about to get punched in the stomach and don’t allow your opposite leg (the one that is remaining flat on the bed) to push into the bed (the movement of hip flexion).

When you raised your hip off the bed this time, did your symptoms change? If so this suggests extension intolerance with a rotational component, meaning your low back is sustaining uneven forces when one leg moves behind you. This can clue someone to why you may have pain when moving into a weightlifting split jerk position!

Load Testing

A simple way to determine if the weight you are lifting (the load) is a trigger for your pain, is to perform a simple weighted front raise screen.¹Start by holding a light dumbbell or kettle bell by your stomach (anything between 5-15 lbs. works great).

Keep your core relaxed and raise the weight out in front of you without your arms bending. What happened to your pain level? If extending the weight caused your back pain, try the same motion again but this time brace your core muscles and then move the weight. Did you notice any difference in your pain levels?

If you noticed your pain was eliminated (or significantly decreased) with the core braced before extending the weight, we can assume your body has an instability problem and the loads you are lifting are leading to your pain. Learning to stiffen your body with purposeful core stability exercises will be key for your recovery.

If however, you still had pain even when bracing your core it means your body is very load intolerant. This means you need to eliminate any weight training and heavy lifting outside of the gym (moving furniture around the house, picking up multiple bags of groceries, etc.) for the time being to allow your back symptoms to calm down.

The last screen called a heel drop test looks into how your body deals with a quick compressive load.^1,3,4 Start by standing on one leg and with your abdominals completely relaxed, raise up on your toes and quickly drop down onto your heel. Do this twice, once with two legs and again with one leg. Did this jarring motion to your spine cause pain?

Now, repeat this test with a small brace of your core. Did you notice anything different?

If bracing your core eliminated your pain when performing the heel drop, you just uncovered a possible reason for why you have pain when performing movements like box jumps, catching a clean or snatch, or when running. Each of these movements loads the spine quickly and your body is not able to handle the load due to the inability to stabilize at the right time.

However, if bracing your core and performing the drop test increased your symptoms, it is a clue that you may be dealing with a possible end plate fracture of your spine. The stiffening of your core added even more compression to the heel drop movement and drove your symptoms to occur. If this is you, eliminating barbell training is a must at this time in order to allow the healing process to occur.

Other Important Tests

Hip Extension Coordination

The next test is designed to see how your body responds during the movement of hip extension (the same movement that occurs at your hip joint when you stand up from a squat, pull a barbell from the floor or propel your body forward during a sprint). For a back to remain healthy, you must have hips that have the ability to generate the appropriate amount of force and fire at the appropriate time. This screen looks into just that and assesses how the muscles that surround your hips (primarily your glute max) work with the low back.

While lying on your back with your knees bent, straighten one leg out and perform a single leg bridge. Hold your hips in the air for 10 seconds and feel for what muscles are working hard to keep you up and if this movement brings out any pain.

What muscles were working hard to keep your hips up? If it was anything other than your glutes (butt muscles) as the primary muscle group you have a coordination issue in how your body is producing hip extension. Research has shown that back pain can often inhibit the activation of your glutes (they basically become turned off and stop functioning correctly).^6,7,19,20 This has been termed to by Dr. Stuart McGill as “gluteal amnesia.”²¹

Did this movement produce pain? As you bridge on one leg, this pain is a response to the uneven forces that are being placed on your back. This is due to the inability of the glutes to kick on appropriately and contribute to hip extension, which means the erectors of your low back have to pull double time. When this happens a ton of force is placed on the spine, which leads to the pain you felt.

If this was you, try to now perform a double leg bridge. Jam your heels into the ground and squeeze your butt muscles as you raise your hips from the ground. Make sure to keep your low back from over arching (don’t raise your hips too high off the ground). Is the pain less than before? If the pain lessens, this demonstrates that your glutes are weak and need to strengthen. Strengthening the glutes to eventually be able to single leg bridge with proper glute activation will be an integral part of your rehab program.

Hip Rotation Assessment

The hips are an area of the body that show a tendency to benefit from increased mobility due to its inclination to become immobile and stiff. If the hips stiffen, they will affect the role of the joint complex directly above (the low back) and cause it to become unstable. For this reason, a thorough evaluation for a back injury must include an assessment of hip mobility!

Research has shown that the rotation of the hips (especially a lack or difference side to side in internal rotation) is a large factor in the development of back pain.^14,15 If an athlete has a significant deficit in internal rotation on one side of the body, the low back will sustain uneven forces as the body drops into the bottom position of a squat, clean or snatch.

To screen for hip internal rotation problems, start by lying on your back. Have a friend grab your leg, bend your knee and lift your thigh to a 60° angle from the bed or floor.

From this position we can rotate the lower leg away from the midline of the body to assess the amount of internal rotation you have. Perform the same movement on both legs. If you could move one leg a few inches away from the midline of the body more than the other, it means you have a significant difference in side-to-side internal rotation

 

Thoracic Spine Mobility Assessment

As we sit all day and use poor posture, our mid back stiffens. If we don’t have adequate mobility in this area, the joint below (the low back) will be forced to move as compensation. This problem is often seen with overhead barbell lifting (snatch, jerk, and the overhead squat).

The seated rotation test (outlined in more detail in this blog: “How To Screen Shoulder Pain“) can give us a good idea of how well your thoracic spine is moving.

Tape an “X” on the ground with the edges forming 90-degree angles. Sit in the middle of the “X” so that the tape forms a “V” in front of you. With a PVC pipe across your chest, rotate as far as you can to the right and left side. Ideally you should be able to rotate your T-spine 45-degrees each way (this will align the PVC pipe with the tape on the ground).^17,18

Classifying Your Back Pain

Based on the above tests, you can now fit your back pain into a specific category.. Understanding how your injury presents will help you understand what things you need to do and what to avoid in the short term to help decrease your symptoms.

If however you felt like you had pain with almost all of the testing, don’t worry! This just means that you are either in the very early stages of the injury (and your back is very sensitive to any movement) and/or the best position for your back is in neutral (neither flexion or extension).

Those who have had a back injury for a long time are often very sensitive to pain.¹³This is actually a neurological overreaction from your brain! Think about how it feels when you stub your big toe. Every small step you take directly after hurts like crazy, because your toe has become overly sensitive to forces placed on it due. This happens to a greater extent with those who have had back pain for more than a few weeks and is why the smallest movements (like bending forward to pick up a bag of groceries or turning over in bed) may set off tremendous pain.

For this reason, in addition to corrective exercises to help support your core and strengthen your body to return to heavy barbell training (things we’ll discuss shortly in the future) we also need to make some small adjustments to your day to day movement habits in order to desensitize and “wind down” your current pain levels.

If you were able to place your back pain into a specific category, here is a few things to keep in mind that can help decrease your pain throughout your day.

Flexion Intolerance

• Signs & Symptoms: Your pain has a tendency to come out when your spine is in a bent or flexed position.
• Guidelines:
  • In bed: don’t sit straight up when getting out of bed. Roll to your side and then push up with your arms. If lying on your stomach feels good, remain on your stomach for a few minutes 2-3 times a day.
  • Sitting: Place a small towel roll under your low back to keep it from rounding. Sit up tall and don’t slouch!
  • Standing: make sure you’re ‘standing tall’ and not slouching throughout your day.
  • Picking things up: instead of bending over to grab something (like clothes out of a laundry basket) kneel down instead to keep your back from rounding.

Extension Intolerance

• Signs & Symptoms: Your pain is associated with extension or over arching your back.
• Guidelines:
  • In bed: if you’re a stomach sleeper, place a pillow under your belly. If you sleep on your back, place a pillow under your knees. Both will help decrease the amount of extension you have in your low back to make sleeping easier and less painful.
  • Sitting: relax your back against the back of a chair, don’t sit on the edge which may cause you to over arch your spine.
  • Standing: stand tall but make sure you’re not over extending your low back.
  • Picking things up: think about moving from your hips more than your low back (emphasize hip extension over low back extension). Kneeling down to pick something off the ground is also helpful.

Rotation with Extension Intolerance

• Signs & Symptoms: Your low back becomes painful when extension is coupled with a rotational or twisting movement.
• Guidelines:
  • In bed: if you’re a side sleeper, place a pillow between your knees. This will limit any rotation at your hips that places uneven forces on your low back. When getting out of bed, roll your legs and trunk together.
  • Sitting: make sure to limit crossing your legs, or leaning/shift to one side or the other.
  • Standing: stand tall on both legs. ‘Hanging out’ on one leg or crossing your legs will again place uneven stress on your low back.
  • Picking things up: make sure to limit excessive rotations in your trunk. Move with your hips/legs, not with your back.

Load Intolerance

• Signs & Symptoms: Your pain comes out when performing physical tasks that load your spine such as lifting weights in the gym, holding multiple bags of groceries or opening a window.
• Guidelines:
  • Avoid performing tasks that require you to lift a load. If you must carry something (like bags of groceries), make sure you use both hands to evenly spread the load.
  • Avoid running or any other tasks that place a load or shock through your body.
  • Tone down your lifting in the gym to only pain-free tasks at this time! Don’t be the tough guy and push through pain, it is only stretching out the time it will take to become pain free.

Can I Still Lift?

During these next few weeks and possibly months, you must consider limiting your heavy training and only exercising with movements that do not create any pain. Pain is not only an annoyance but it also changes how you move.⁹

This means the back pain you are currently experiencing is hurting your ability to use good technique when lifting. Not only does this have direct implications on your performance, but training through pain and loading your body with compromised technique can continue the injury process.

I have worked with many athletes who have continued to push through heavy training programming while dealing with back pain. It did not end well. If you want to eliminate your pain and return to high performance lifting, you must tone down any lifting that creates pain at this time.

Final Thoughts

By now I hope you have now been able to find the exact pain trigger for your back pain. Remember, most back pain is due to a repeated posture, motion or load that eventually leads to injury. Trying to modify and eliminate these particular motions, postures or loads that causes back pain and replacing them with those that feel good is the first step in fixing your pain.

You are now in the drivers seat and how you use your body throughout your day will determine whether you have pain, or not! Stuart McGill wrote, “during recovery, what you don’t do is often just as important as what you do do.” Remember this motto as you begin your journey to eliminate your pain and return to the things you love to do. Now that we have newfound knowledge of what creates and eliminates pain, we can start to craft together an efficient rehabilitation plan that is right for your body! This will be our topic of next week’s blog!

If your pain however does not fit into any of the above categories oryou are also experiencing a recent unintentional loss in weight, incontinence, pain in your abdomen or pelvic floor, I highly recommend you make an appointment to see your doctor. If you have any of these signs, it may mean that you have a serious illness that could present like mechanical low back pain. If you have any doubt at all, please see a medical doctor!

Until next time,

With

References

1. McGill, SM. Back Mechanic: The step by step McGill Method to fix back pain. Backfitpro Inc. 2015
2. Sahrmann S, Azevedo DC & Van Dillen L. Diagnosis and treatment of movement system impairment syndromes. Braz J Phys Ther. 2017; 21(6):391-399
3. Hertling D & Kessler RM. Management of Common Musculoskeletal Disorders: Physical Therapy Principles and Methods. Philadelphia: J.B. Lippincott, 1996. Print.
4. Robinson HS, Brox JI, Robinson R, Bjelland E, et al. The reliability of selected motion- and pain provocation tests for the sacroiliac joint. Manual Therapy. 2007;12:72-79
5. Van Dillen LR, Sahrmann SA, Norton BJ, Caldwell CA, McDonnell MK, Bloom NJ. Movement system impairment-based categories for low back pain: stage 1 validation. J Orthop Sports Phys Ther. 2003;33(3):126-42
6. Freeman S, Mascia A, McGill SM. Arthrogenic neuromuscular inhibition: a foundational investigation of existence in the hip joint. Clin Biomech. 2013; 28:171-77.
7. Bullock-Saxton JE, Janda V, Bullock MI. Reflex activation of gluteal muscles in walking. An approach to restoration of muscle function for patients with low-back pain. Spine. 1993;18(6):704-8
8. Leinonen V, Kankaanpaa M, Airaksinen O, Hannien O. Back and hip extensor activities during trunk flexion/extension: effects of low back pain and rehabilitation. Arch Phys Med Rehabil. 2000;81(1):32-7
9. O’Sullivan P. Diagnosis and classification of chronic low back pain disorders: maladaptive movement motor control impairments as underlying mechanism. Man Ther. 2005;10(4):242-55
10. McKean, M. R., Dunn, P. K., & Burkett, B. J. (2010). The lumbar and sacrum movement pattern during the back squat exercise. The Journal of Strength & Conditioning Research, 24(10), 2731-2741.
11. List, R., Gülay, T., Stoop, M., & Lorenzetti, S. (2013). Kinematics of the trunk and the lower extremities during restricted and unrestricted squats. The Journal of Strength & Conditioning Research, 27(6), 1529-1538.
12. Campos, M. H., Aleman, L. I., Seffrin-Neto, A. A., Vieira, C. A., DE Paula, M. C., & DE Lira, C. A. (2016). The geometric curvature of the lumbar spine during restricted and unrestricted squats. The Journal of Sports Medicine and Physical Fitness.
13. Giesecke T, Gracely RH, Grant M AB, et al. Evidence of augmented central pain processing in idiopathic chronic low back pain. Arthritis & Rheumatism. 2004; 50(2):613-623
14. Sadeghisani M, Manshadi FD, Kalantari KK, et al. Correlation between hip range-of-motion impairment and low back pain. A literature review. Orthop Traumatol Rehabil. 2015;17(5):455-62
15. Almeida GP, da Souza VL, Sano SS, et al. Comparison of hip rotation range of motion in judo atheltes with and without history of low back pain. Man Ther 2012; 17(3):231-5
16. Brinjikji W, Luetmer PH, Comstock B, et al. Systematic literature review of imaging features of spinal degeneration in asymptomatic populations. Am J Neuroradiol. 2015;36:811-16
17. Johnson KD, Kim KM, Yu BK, Saliba SA, et al. Reliability of thoracic spine rotation range-of-motion measurements in healthy adults. J Athl Train. 2012;47(1):52-60
18. Johnson KD, Grindstaff TL. Thoracic rotation measurement techniques: clinical commentary. N Am J Sports Phys Ther. 2010;5(4):252-6
19. Nelson-Wong E, Alex B, Csepe D, Lancaster D, Callaghan JP. Altered muscle recruitment during extension from trunk flexion in low back pain developers. Clin Biomech. 2012;27(10):994-8
20. Leinonen V, Kankaanpää M, Airaksinen O, Hänninen O. Back and hip extensor activities during trunk flexion/extension: effects of low back pain and rehabilitation. Arch Phys Med Rehabil. 2000;81(1):32-7
21. McGill SM. Ultimate Back Fitness and Performance (4^thed). Waterloo, Canada: Backfitpro Inc, 2009. (www.backfitpro.com)