The Relationship Between Sagittal Standing Posture and Low Back Pain

Justin Gibson, BS, CSCS

Introduction

            Low back pain is a common and often debilitating condition affecting an average of 12% of all persons at any given time and a lifetime prevalence upwards of 60% of the population across sex, socioeconomic, occupational, and national boundaries (Hoy, et al., 2012). Researchers the world over have searched for underlying causes and contributing factors to low back pain, and the methods and results they have obtained vary substantially from one study to the next.

            One such potential factor is posture. The position and alignment of the lumbar vertebrae is a logical point of interest when studying pain in the region, and as such has been the focal point of many researchers. However, the literature surrounding posture and low back pain is complicated, with a great deal of variety in both defining “posture” and “pain”, and a consensus among researchers is often illusive. In this paper, I will attempt to provide an overview of major studies in the realm of static standing posture in the sagittal plane and its link -or lack thereof- to pain.

Posture and Low Back Pain: The Theory

            All studies begin with a question based on a thorough analysis of the research that came before them. To ask the question, “Does one’s posture affect their risk of developing lower back pain?”, there must be a reasonable theory behind why that might be the case. And, indeed, many studies and textbooks have put forth potential structural and physiological factors linking the two.

            In their study, “Effect of low back posture on the morphology of the spinal canal”, Chung, Lee, Kim, Chung, & Ahn (2000) observed structural changes in the spine when subjects were placed in differing positions during MRI imaging of 20 healthy young volunteers. Using foam bolsters and stabilization belts, the researchers looked at L3-L4 and L4-L5 relationships when subjects were put into neutral, flexed, extended, and rotated positions. They found that the gap between the posterior disc and the anterior margin of the facet joint increased with flexion and decreased with extension or rotation. This narrowing of the spinal canal during extension and rotation, the researchers argued, could potentially explain the posture-dependent symptom of spinal stenosis. However, the authors of this study acknowledge the limitations of measuring the behavior of the spine in a cramped MRI machine, including a restriction of range of motion and the inability to axially load the spine. Still, changes in the spinal canal were observed, and give some credence to the link between certain spinal ailments and certain postures.

            Another study that looked at potential risk factors for postural aberrations was performed by Burnett et al on female rowers. A non-invasive electromagnetic device was attatched at L3 and S2 to measure axial rotation range of motion in different circumstances. For both standing and sitting, subjects achieved the highest degree of rotation in a “neutral zone” determined by the experience physiotherapists guiding the study to be the midpoint between end-range flexion and extension. When the subjects were guided into end-range extension, axial rotation was significantly reduced; the researchers theorized that this was due to the bony stiffness provided by the facet joints of the vertebra. In end-range flexion, axial rotation was even more significantly reduced, this time possibly due to passive stiffness from the posterior fibers of the annulus and the posterior ligaments. The results of the study suggest that in end-ranges of motion, more force may be absorbed by the comparitively less resilient passive structures of the spine rather than the active, muscular structures, and could potentially lead to injury.

            While these studies are useful in determining potential mechanisms for injury during significant flexion or extension, they say little about “natural” standing posture, as most people do not stand with their spines approaching end ranges of either flexion or extension. In fact, “natural” standing postures can be frustrating to study due to the immense variance between individuals. Such was the goal of Claeys, Brumagne, Deklerck, Vanderhaeghen, & Dankaerts (2016) when they attempted to look at correlations between all spinal regions in 99 healthy first year physiotherapy students. These researchers looked at lumbar curve, thoracic inclination, trunk angle, pelvic tilt, lumbar angle, head angle, neck angle, and cervicothoracic angle to any and all correlations between them. What they found with respect to standing posture was that only trunk angle was significantly predictive of other angles, and even then, the correlations were mostly medium to small. In discussing their findings, the authors conclude that optimal posture probably does not exist in a way that can be applied to any large population, and the “optimal” posture for any individual will be heavily determined by genetic and environmental factors unique to them.

            Lastly, even though perfect posture may be undefinable for the population as a whole, we can at least identify certain patterns in standing postures that make defining different postures possible. Researchers appear to have no set consensus on what categories of sagittal plane posture should exist, and the studies presented in this paper use a mixture of quantitative and categorical variables in attempting to do so. One such category of standing posture is sway, which is seen in O'Sullivan, et al. (2002) and in Smith, O'Sullivan, & Straker (2008) and is defined, loosely, as an anterior shifting of the pelvis resulting in a posterior trunk lean. In the former study, muscular activity was measured in sway standing as compared to neutral standing (neutral, here, was defined as having markers on the acromion, greater trochanter, and lateral malleolus stacked in a straight line on top of one another). Sway posture was of interest to the study because it was deemed a “passive” posture that one might adopt to save energy by relying on passive structures of the body rather than active ones, akin to a slumped sitting posture (which was also measured in this study). The researchers found that muscle activity changed dramatically between neutral and sway postures: the lumbar multifidus, internal oblique, and thoracic erector spinae all showed a significantly decreased activations  when the subject shifted into the sway posture, replaced by a significant increase in rectus abdominus activity. When discussing the clinical relavence of these findings, the researchers speculate that individuals who habitually adopt passive postures deactivate and potentially decondition the stabilizing muscles of the lumbopelvic region, which may leave it vulnerable to strain, instability, or injury.

            To summarize the theory behind looking at the relationship between posture and low back pain, we see in the research that as the spine moves further away from “neutral” postures (individualistic though they may be), it relies more on passive structures to absorb force rather than the more resilient active structures. These deviations may also decrease the space in the spinal canal, which can potentially increase the risk of certain spinal ailments such as stenosis. However, most individuals do not approach end-ranges of motion in their normal standing posture, and as such the happenings-on at these ranges may be of limited use.

Correlations in Observational Studies

            Though flawed, there is enough evidence linking posture to potential mechanisms of low back pain to have warranted many studies on the subject. The most common way to study most correlations is through observational studies, which attempt to find commonalties between or across groups at a set point in time, without establishing any cause an effect relationship. Though not experiments, they can be useful in identifying potential links between two variables.

            An author of one of our previous studies about sway postures, O’Sullivan, who also took part in a similar study linking that posture and others to low back pain in adolescents. Specifically, the authors divided subjects into sway, flat, hyperlordotic, and neutral categories. What they found was interesting: subjects with non-neutral postures demonstrated higher odds for all measures of back pain, but no one posture was consistently associated with pain in isolation (Smith, O'Sullivan, & Straker, 2008). For instance, males with sway posture were more likely to have back pain lasting three months or more, but females with this same posture were no more likely to experience pain than those with neutral posture. Likewise, females with a flat posture were more likely to have pain aggravated by sport, but males were not.

            Indeed, the issue seems to be more complicated than a one-to-one relationship between static standing posture and low back pain. A different study on adolescents showed no correlations between postural displacements and back pain using the PosturePrint internet-based computer system (Ozyurek, Genc, Karaali, & Algun, 2017). One study finds an association with a loss of lumbar lordosis (Jackson & McManus, 1994), and another study finds an association with an increase in lumbar lordosis (Christie, Kumar, & Warren, 1995).

            One study, refreshingly titled “Low Back Pain and Posture” (Tuzun, Yorulmaz, Cindas, & Vatan, 1999) grouped subjects into acute pain, chronic pain, and a pain-free control groups of 50 each, then measured their degrees of thoracic kyphosis, lumbar lordosis, and sacral inclination in a relaxed standing posture with no shoes. Some correlations were found between age and thoracic kyphosis, and between BMI and lumbar lordosis. However, when comparing these postural angles between the subject groups, the researchers detected no statistically significant differences. In their conclusion, the researchers state that it is not reasonable to make a generalization regarding these angles and low back pain.

            This is not to say, however, that the two are unrelated. Three possible explanations were offered by Christie, Kumar, and Warren, who were mentioned above. They found that those in acute pain were more likely to have greater thoracic kyphosis and forward head positions, and that chronic back pain sufferers showed significantly greater lumbar lordosis. The postural parameters they studied only had moderate value in the prediction of pain, and they would not state whether posture lead to pain or precipitation of pain causes postural aberrations. Instead, they offer three possible explanations for the correlations they found:

1.With the onset of pain, all aspects of the spinal curve initially respond to the pain with increased forward head posture to decrease lumbar pain

2. Individuals with acute low back pain may have had a preexisting FHP that resulted in flexion of the T spine and signs and symptoms in the lumbar spine

3. Chronic LBP sufferers have adapted to the pain with a localization of the postural changes the lumbar spine that balances the upper spine back towards normal.

            The lack of consensus in these studies are probably due to the fact that methodologies for measuring posture, pain, or both varied significantly between one study and the next. For example, our two studies on adolescents came to different conclusions: one took a relatively simple measurement of posture, administered a simple yes/no questionnaire on lifetime back pain, and got no correlation (Ozyurek, Genc, Karaali, & Algun, 2017); the other took a more detailed questionnaire inquiring into different types of pain and correlated that with specific postures, separated further by male and female, and got the more nuanced results discussed earlier (Smith, O'Sullivan, & Straker, 2008). Perhaps both “posture” and “low back pain” are simply not specific enough terms on their own to ensure consistent definitions and methodologies across a broad range of studies. As Christie et al put it, “Ideal posture has not been universally agreed to and several different definitions have been advanced.” However, classifications of ‘neutral’, ‘hyperlordotic’, ‘flat’, and ‘sway’ have been used by several authors in several studies: O'Sullivan, et al., 2002, Smith, O'Sullivan, & Straker, 2008, and Christie, Kumar, & Warren, 1995, so perhaps there is still enough consistency to make useful comparisons.

­Longitudinal Studies on Posture and Low Back Pain

            Longitudinal experiments are widely considered to be the gold standard at establishing cause and effect in a population. However, the time and monetary commitment they require make them more prohibitive than observational studies. The following two studies took a baseline measurement of a subject pool, then followed those same subjects over a period of time to see the long-term impacts, if any, of a multitude of factors, including posture.

            Widhe, 2001 measured the thoracic kyphosis, lumbar lordosis, spinal mobility, and incidences of back pain in a group of 90 children at ages 5 and 6, and then again at ages 15 and 16. He found that posture did change significantly during the study period: both thoracic kyphosis and lumbar lordosis increased by roughly 6°, and gender differences that were not present at ages 5-6 presented themselves at age 15-16. He also found that mobility significantly decreased during the 10 years between measurements, particularly in the thoracic spine. Finally, he reported that about one-third of the children at 15-16 stated that they had occasional low back, which was similar to other reports using comparable methods. However, these incidences of low back pain were not related to posture, spinal mobility, or even physical activity in the sample population he took.

            Widhe offers some insights into his findings. He suggests that the sharp rise in the prevalence of low back pain between pre-pubescence and puberty could reflect the transition from “living in the present” to “bodily awareness”; the pain may not be a pathological condition of the spine itself, but a new dimension of the mind. This, he states, may explain why it has been hard to find any “physical parameters” predicting future low back pain. He also contrasts LBP in youngsters and adults, as the definition of back pain in the latter group is often defined by its consequences, such as work incapacity, as opposed to simply pain and discomfort.

            For a perspective on adults, Adams et al., 1999 followed 403 healthcare workers aged 18-40 for three years, with initial testing that included functional assessments of anthropometry, muscle strength and endurance, mobility, and posture, as well as psychological assessment via the MSPQ+ZUNG. The subjects also answered a questionnaire every 6 months to check for low back pain. The study found the following to be consistent predictors of low back pain: reduced range of lumbar lateral bending, a long back, reduced lumbar lordosis, increased psychological distress (measured by the MSPQ+ZUNG), and previous nonserious low back pain. Only the latter three were consistent predictors of “any” back pain.

            However, even in a longitudinal study, correlation still does not equal causation. The results of the study state that these factors were much better predictors of low back pain than chance alone, but even when combined (posture was only one of many factors considered predictive) the researches only obtained an R² % value of 11.6. This means that less than 12% of the volunteers studied could attribute their back pain to any of the psychological or physical risk factors considered in the study. Under the section of their article titled “What Caused Most of the Back Pain?”, the researchers wrote: “Despite these possibilities, it is becoming apparent that there are no simple explanations for LBP, only a large number of interacting causes that must be identified and pieced together like a jig-saw puzzle. As far as relatively trivial LBP is concerned, the effort to pursue these causes may simply not be worthwhile, because the failure of all the physical factors to predict “any” LBP in the current study surely indicates that mechanical influences in the reporting of such pain are negligible.”

Conclusion

            Posture is a complicated topic that, despite having a general consensus around “neutral” being better, researchers have been yet to quantify in exact terms. Low back pain is an enormously complex subject that not only has a plethora of physical factors to consider, but psychological, social, and environmental factors as well. Without a concrete understanding of the complexities of either, it is very difficult to make accurate predictions about the relationship between low back pain and posture to a large population, and harder still to apply these broad concepts in a clinical setting where possibly the only firmly established truth about either is that they are both highly individualized. It is my opinion that static standing posture has not been proven to be a reliable predictor of low back pain, and that dynamic postures and loading probably play a more significant role.

           

           

References

Adams, M., Mannion, A., & Dolan, P. (1999). Personal Risk Factors for First-Time Low Back Pain. Spine, 2497-2505.

Burnett, A., O'Sullivan, P., Ankarberg, L., Gooding, M., Nelis, R., Offermann, F., & Persson, J. (2008). Lower lumbar spine axial rotation is reduced in end-range sagittal postures when compared to a neutral spine posture. Manual Therapy, 300-306.

Cadar, I., & Pop, L. (2015). Correlations between cervical spine posture and low back pain. Human & Veterinary Medicine, 178-181.

Christie, H., Kumar, S., & Warren, S. (1995). Postural Aberrations in Low Back Pain. Archives of Physical Medicine and Rehabilitation, 218-224.

Chung, S., Lee, C., Kim, S., Chung, M., & Ahn, J. (2000). Effect of low back posure on the morphology of the spinal canal. Skeletal Radiology, 217-223.

Claeys, K., Brumagne, S., Deklerck, J., Vanderhaeghen, J., & Dankaerts, W. (2016). Sagittal evaluation of usual standing and sitting spinal posture. Journal of Bodywork and Movement Therapies, 326-333.

Hoy, D., Bain, C., Williams, G., March, L., Brooks, P. B., Woolf, A., . . . Buchbinder, R. (2012). A Systematic Review of the Global Prevalence of Low Back Pain. Arthritis & Rheumatism, 2028-2037.

Jackson, R., & McManus, A. (1994). Radiographic Analysis of Sagittal Plance Alignment and Balance in Standing Volunteers and Patients with Low Back Pain Matched for Age, Sex, and Size. Spine, 1611-1618.

O'Sullivan, P., Grahamslaw, K., Kendell, M., Lapenskie, S., Moller, N., & Richards, K. (2002). The Effect of Different Standing and Sitting Postures on Trunk Muscle Activity in a Pain-Free Population. Spine, 1238-1244.

Ozyurek, S., Genc, A., Karaali, H., & Algun, Z. (2017). Three-dimensional evaluation of pelvic posture in adolescents with and without a history of low back pain. Turkish Journal of Medical Sciences, 1885-1893.

Pillastrini, P., Mugnai, R., Bertozzi, L., Costi, S., Curti, S., Guccione, A., . . . Violante, F. (2010). Effectiveness of an ergonomic intervention on work-related posture and low back pain in video display terminal operators: A 3 year cross-over trial. Applied Ergonomics, 136-443.

Smith, A., O'Sullivan, P., & Straker, L. (2008). Classifcaton of Sagittal Thoraco-Lumbo-Pelvic Alignment of the Adolescent Spine in Standing and Its Relationship to Low Back Pain. Spine, 2101-2107.

Tuzun, C., Yorulmaz, L., Cindas, A., & Vatan, S. (1999). Low Back Pain and Posture. Clinical Rheumatology, 308-312.

Widhe, T. (2001). Spine: Posture, mobility and pain. A longitudinal study from childhood to adolescence. European Spine Journal, 188-123.

Poor Shoulder External-to-Internal Strength Ratios Found to Increase Injury Risk in Overhead Athletes and Their Applicability to Recreational Weight Training Populations

Justin Gibson, BS, CSCS

Introduction

Shoulder performance and injury is a major topic of interest for professional athletes, recreational fitness enthusiasts, and the general population alike. Whether discussing one’s ability to throw a baseball at a consistently high velocity or their ability to hoist a gallon of milk onto a countertop, the strength and health of the glenohumeral joint should and has been the subject of a large body of scientific literature. However, when seeking funding for a research proposal, it is perhaps easier to justify studying a shoulder when it is attached to a body on a $3.1 million dollar 2-year contract than it would be if it were attached to someone lifting weights as a hobby. And so, a large proportion of our scientific literature regarding the shoulder tends to focus on athletes, specifically overhead athletes, when attempting to identify potential risk factors for injury.

          One such risk factor explored in these studies has been the balance between external rotation strength of the shoulder and internal rotation strength. For overhead athletes in particular, it is believed that the eccentric strength of the external rotators should be as strong as the concentric strength of the internal rotators to maintain glenohumeral stability and optimal shoulder function (Wang & Cochrane, 2001). In this paper, I will discuss the scientific evidence linking internal/external rotator imbalance as a predictor of injury in overhead athletes, the similarities between these athletes and recreational weightlifters, and possible data that may build a bridge between them.

External/Internal Rotation Strength Ratios as a Predictor for Injury in Overhead Athletes

          Several studies have noted a link between shoulder muscle imbalance and injury. Two such studies looked at several factors that may contribute to shoulder injury: range of motion, external rotation weakness, scapular asymmetry, and ER/IR strength ratios. Clarsen, Bahr, Anderson, Munk, & Myklebust (2014) measured all of these factors when following the teams in the Norwegian elite handball series for men for three months of the 2011-2012 season. They found significant associations between ER weakness, obvious scapular dyskinesis, and shoulder range of motion, and inury, and “noteworthy” associations between injury and ER/IR strength ratios. To directly quote the study, “non-significant trends in the data suggest that lower ER to IR ratios and abduction strength may also be noteworthy risk factors.”

 In contrast, Wang & Cochrane (2001), in their study on elite male volleyball players, concluded that shoulder rotator muscle strength imbalance (eccentric external/concentric internal <1) played in statistically significant role in the shoulder injuries of their athletes over the course of their season, whereas shoulder mobility, scapular asymmetry, and muscle strength were not significantly associated with injury.  These two studies each have their merits and limitations: The Clarsen study follows a larger group of athletes, while the Wang study measures a longer timeframe. Both studies, however, at least make note of the ER/IR ratios as a risk factor, and both studies extensively reference other studies done on overhead athletes when discussing possible causes of injury.

          Perhaps stronger evidence for the link between ER/IR imbalance and injury is seen in Bryam, et al. (2010). While the researchers’ hypothesis mainly concerned the weakness of shoulder external rotators (which they found to be very strongly associated with injury), they also found significant links between low ER/IR strength and overall throwing injuries and an even stronger association with shoulder injuries specifically. This study was conducted over a 5 year period at looked at 144 Major and Minor League Baseball pitchers, a much larger scope than the previous two studies (and with, as noted earlier, more expensive subjects).

          All three of these studies discuss, independent of their findings, why a proper ER/IR strength ratio may be important in predicting injury. Handball, volleyball, and baseball all involve motions that require significant internal rotation torque to perform at a high level, and as a result, these athletes tend to develop very strong internal rotators without a concurrent strengthening of their external rotators (Codine, L., Pocholle, Benaim, & Brun, 1997). In a high-velocity activity such as throwing, this imbalance may lead to soft tissue injuries as the weak external rotators are unable to provide enough stability to the glenohumeral joint to counteract the immense forces produced by the internal rotators. With this in mind, are these findings relevant to the average weight lifter, or do they only apply to the specific motions of overhead athletes?

The Role of the Rotator Cuff in Glenohumeral Stability and Movement

          Thus far this paper has not attributed internal or external rotation to any specific muscle or muscle group, but of course these motions are achieved by the contraction of specific muscles. Most anatomy textbooks attribute internal rotation to the subscapularis of the rotator cuff, with the larger pectoralis major, anterior deltoid, and latissimus dorsi muscles contributing significantly. The posterior muscles of the rotator cuff, the infraspinatus and the teres minor, are the external rotators, with only the posterior deltoid providing significant additional force, although some studies also suggest the supraspinatus could play a significant role (Dark, Ginn, & Halaki, 2007). This difference in cross-sectional area of muscles that provide internal rotation vs. external rotation could explain why even in non-athletes, internal rotation strength is significantly higher (Noffal, 2003).

          Rotation, however, is not the only function of the rotator cuff. It could be argued that their isometric role in stabilizing the humeral head in the glenoid fossa is as or more important than their isotonic role in providing rotation. Centering the axis of rotation in the glenohumeral joint could be an important factor in preventing shoulder impingement, and it is a role for which the rotator cuff muscles, particularly the inferior and posterior components, are well suited (Sharkey & Marder, 1995). Indeed, instability of the shoulder joint has been shown to be a major predictor of injury in overhead athletes and weightlifters (Gross, Brenner, Esformes, & Sonzogni, 1993).

Applying ER/IR Strength Ratios to the Weight Training Population

          Now that we have established some evidence that a lack of external rotation strength compared to internal rotation strength has been observed to predict injury in overhead athletes, and that specific muscles are responsible for these actions, we can begin attempting to link this information to the recreationally trained weight lifting population. Some common ground has been found between the ER/IR strength ratios of throwers and recreational weight lifters. When comparing throwers to non-throwers, Codine, L. et al (1997) and Noffal (2003) found that throwers had a lower concentric ER/IR strength ratio (about 0.57 and 0.65 at 300 degrees/second, respectively) than non-throwers (about 0.75 at 300 degrees/second in both studies) in their dominant throwing arms, and that this was due to the throwers’ higher IR strength without a significant increase of ER strength over non-throwers.

A similar study which looked at muscluar strength differences between the recreational weight training population and a control group found that these same ER/IR strength discrepencies also exist in the recreational weight training population (about 0.61), and that this imbalance is also due to a strengthening of the internal rotators without concurrent strengthening of the external rotators (Kolber, Beekhuizen, Cheng, & Hellman, 2009). In EMG studies, the pectoralis major, commonly targeted in traditional weight training programs, has been shown to contribute significantly to internal rotation (achieving similar activation rates as the subscapularis), whereas no such large muscle is activated nearly to the same extent as the infraspinatus during external activation (Dark et al, 2007).

          Shoulder instability, particularly anterior shoulder instability, has been observed in weight lifters with shoulder pain. Gross, et al (1993) observed that every patient in their study (all of whom had recurrent instability in one or both shoulders and reported weight lifting as their primary recreational activity) experienced pain in abducted and externally rotated positions when the humeral head is translated anteriorly in the glenoid fossa, and that most of them could not recall any particular event that caused the pain.  In common weight training exercises such as the bench press and row, the rotator cuff functions in a reciprocal fashion to oppose translation of the humeral head by the larger external muscles acting on the shoulder; the infraspinatus is highly active during the bench press to oppose the pectoralis major’s anterior pull, and the subscapularis is highly active during the row to oppose the latissimus dorsi’s posterior pull (Wattanaprakornkul, Halaki, Cathers, & Ginn, 2011). However, as noted in the Kolber study, there is little evidence to suggest that the infraspinatus is significantly strengthened alongside the larger pectoralis major in most common resistance training programs. This may provide a possible explanation as to why some recreational weight lifters experience progressive shoulder pain: large muscles such as the pectoralis major are strengthened at much faster rates and have a much larger total strength capacity than the muscles of the posterior rotator cuff, and eventually these smaller intrinsic muscles cannot adequately stabilize the glenohumeral joint during exercises like the bench press.

Shoulder Injury Prevention in Weight Training Populations and the Case for More Research

          Although not common in traditional weight training programs, the infraspinatus and other rotator cuff muscles can be specifically targeted and relatively isolated from other muscles with the right exercises (Escamilla, Yamashiro, Paulos, & Andrews, 2009). Properly designed strength training programs that include exercises to specifically target external rotators can limit or eliminate the ER/IR strength discrepancy found to be common in weight lifters (Niederbracht, Shim, Sloniger, Paternostro-Bayles, & Short, 2008).

          It is important, however, to note that the comparison between throwing athletes, recreational weight lifters, and the methods used to measure their respective muscle imbalances, has several caveats and outright flaws that need to be addressed. Testing methods for ER/IR rotation varied across the studies I’ve presented in this paper; Bryam (2010), Clarsen (2014), and Kolber (2009) all used isometric testing protocols to measure ER/IR strength, whereas Wang (2001), Codine (1997), Noffal (2003) used isokinetic testing. This is important to note because the sports played by the athletes in the study involve dynamic, rather than isometric, motions of the shoulder, often under immense load and stress. Baker, Wilson, & Carlyon (1994) found that while isometric and dynamic measurements of strength are significantly related, they were not so closely related to imply generality of muscle strength across all contraction types and speeds. It would not be advisable to assume that isometric strength is always going to predict high-velocity eccentric strength, or that changes in isometric strength over the course of a strength training program always reflect dynamic changes in strength.

          Isometric testing, however, may be appropriate for testing the strength of the infraspinatus in recreational weight lifters. As previously stated by Wattanaprakornkul (2011), the infraspinatus plays a major isometric role in glenohumeral joint centration during the bench press as it opposes anterior translation, which contributes to anterior instability. I would make the case that measuring the isometric ER/IR strength ratios of recreational weight lifters might be an effective estimate their posterior rotator cuff’s ability to maintain glenohumeral stability against the pull of the pectoralis major during popular exercises like the bench press. Studies referred to in this paper have only looked at these ER/IR strength imbalances as they relate to overhead athletes, and further study would be recommended to see if such a correlation exists in the recreational weight training population.

Conclusion

The connection between low external-to-internal rotation strength of the shoulder and risk of injury has been well documented in throwing and overhead athletes, and the need to maintain proper balance between the two has been the objective of many strength and conditioning programs for athletes of all levels. Low ER/IR strength ratios similar to that of overhead athletes have also been observed in recreational weight lifters. Considering the dual role of the rotator cuff as shoulder rotators and shoulder stabilizers, and that traditional strength training tends to neglect the external rotators, more research needs to be done to determine whether this same ER/IR strength discrepancy when present in weight lifters carries the same risk of injury.

         

         

Bibliography

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Bryam, I. R., Bushnesll, B. D., Dugger, K., Charron, K., Harrell, F. E., & & Noonan, T. J. (2010). Presason Shoulder Strength Measurements in Professional Baseball Pitchers. The American Journal of Sports Medicine, 1375-1382.

Clarsen, B., Bahr, R., Anderson, S. H., Munk, R., & & Myklebust, G. (2014). Reduced Glenohumeral Rotation, External Rotation Weakness and Scapular Dyskinesis Are Risk Factors for Shoulder Injuries Among Elite Male Handball Players: A Prospective Cohort Study. Br J Sports Med.

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Kolber, M., Beekhuizen, K., Cheng, M., & & Hellman, M. (2009). Shoulder Joint and Muscle Characteristics in the Recreational Weight Training Population. Journal of Strength and Conditioning Research, 148-157.

Niederbracht, Y., Shim, A. L., Sloniger, M. A., Paternostro-Bayles, M., & & Short, T. (2008). Effects of a Shoulder Injury Prevention Strength Training Program on Eccentric External Rotator Muscle Strength and Glenohumeral Joint Imbalance in Female Overhead Activity Athletes. Journal of Strength and Conditioning Research, 140-145.

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Wang, H.-K., & Cochrane, T. (2001). Mobility impairment, muscle imbalance, muscle weakness, scapular asymmetry and shoulder injury in elite volleyball athletes. The Journal of Sports Medicine and Physical Fitness, 403-410.

Wattanaprakornkul, D., Halaki, M., Cathers, I., & & Ginn, K. A. (2011). Diretion-Specific Recruitment of Rotator Cuff Muscles During Bench Press and Row. Journal of Electromyography and Kinesiology, 1041-1049.