Electromyography Activation of Shoulder and Trunk Muscles is Greater During Closed Chain Compared to Open Chain Exercises

Background To compare the activation of shoulder and trunk muscles between six pairs of closed (CC) and open chain (OC) exercises for the upper extremity, matched for performance characteristics. The secondary aims were to compare shoulder and trunk muscle activation and shoulder activation ratios during each pair of CC and OC exercise. Methods Twenty-two healthy young adults were recruited. During visit 1, the 5-repetition maximum resistance was established for each CC and OC exercise. During visit 2, electromyography activation from the infraspinatus (INF), deltoid (DEL), serratus anterior (SA), upper, middle and lower trapezius (UT, MT, LT), erector spinae (ES) and external oblique (EO) muscles was collected during 5-repetition max of each exercise. Average activation was calculated during the concentric and eccentric phases of each exercises. Activation ratios (DEL/INF, UT/LT, UT/MT, UT/SA) were also calculated. Linear mixed models compared the activation by muscle collapsed across CC and OC exercises. A paired t-test compared the activation of each muscle and the activation ratios (DEL/INF, UT/LT, UT/MT, UT/SA) between each pair of CC and OC exercises. Results The INF, LT, ES, and EO had greater activation during both concentric (p = 0.03) and eccentric (p \u3c 0.01) phases of CC versus OC exercises. Activation ratios were lower in CC exercises compared to OC exercises (DEL/INF, 3 pairs; UT/LT, 2 pairs; UT/MT, 1 pair; UT/SA, 3 pairs). Conclusion Upper extremity CC exercises generated greater activation of shoulder and trunk muscles compared to OC exercises. Some of the CC exercises produced lower activation ratios compared to OC exercises

USAGE AND ACCEPTABIITY OF DATA NORMALIZATION IN BASEBALL PITCHING

To account for athletes of different sizes, kinetic values are commonly ‘normalized’ by dividing by mass and/or height. However, the creation of a ratio variable requires certain statistical assumptions to be met. The purpose of this study was to determine if elbow valgus torque predicted by pitching velocity is influenced by the normalization method using regression model comparison with normalized torque values. Both mass and mass*height normalization satisfied the correlation and zero intercept assumptions. Results did not agree between analysis methods that elbow valgus torque could be predicted with pitching velocity at the α = 0.05 level, indicating caution should be exercised before normalizing pitching kinetics data without confirming the assumptions for a ratio variable are met

Supraspinatus tendon micromorphology in individuals with subacromial pain syndrome

Study Design: Cross-sectional cohort. Introduction: Tendon collagen organization can be estimated by peak spatial frequency radius (PSFR) on ultrasound images. Characterizing PSFR can define the contribution of collagen disruption to shoulder symptoms. Purpose of the Study: The purpose of this was to characterize the (1) supraspinatus tendon PSFR in participants with sub acromial pain syndrome (SPS) and healthy controls; (2) PSFR between participants grouped on a tendon visual quality score; and (3) relationship between PSFR with patient-reported pain, function, and shoulder strength. Methods: Participants with SPS (n ¼ 20) and age, sex, and arm-dominance matched healthy controls (n ¼ 20) completed strength testing in scaption and external rotation, and patient-reported pain, and functional outcomes. Supraspinatus tendon ultrasound images were acquired, and PSFR was calculated for a region of interest 15 mm medial to the supraspinatus footprint. PSFR was compared between groups using an independent t-test and an analysis of variance to compare between 3 groups for visually qualitatively rated tendon abnormalities. Relationships between PSFR with pain, function, and strength were assessed using Pearson correlation coefficient. Results: Supraspinatus tendon PSFR was not different between groups (P ¼ .190) or tendon qualitative ratings (P ¼ .556). No relationship was found between PSFR and pain, functional loss, and strength (P \u3e .05). Conclusions: Collagen disruption (PSFR) measured via ultrasound images of the supraspinatus tendon was not different between participants with SPS or in those with visually rated tendon defects. PSFR is not related to shoulder pain, function, and strength, suggesting that supraspinatus tendon collagen disorganization may not be a contributing factor to shoulder SPS. However, collagen disruption may not be isolated to a single region of interest. Level of Evidence: 3b: case-control study

Head and shoulder posture affect scapular mechanics and muscle activity in overhead tasks

Forward head and rounded shoulder posture (FHRSP) is theorized to contribute to alterations in scapular kinematics and muscle activity leading to the development of shoulder pain. However, reported differences in scapular kinematics and muscle activity in those with forward head and rounded shoulder posture are confounded by the presence of shoulder pain. Therefore, the purpose of this study was to compare scapular kinematics and muscle activity in individuals free from shoulder pain, with and without FHRSP. Eighty volunteers were classified as having FHRSP or ideal posture. Scapular kinematics were collected concurrently with muscle activity from the upper and lower trapezius as well as the serratus anterior muscles during a loaded flexion and overhead reaching task using an electromagnetic tracking system and surface electromyography. Separate mixed model analyses of variance were used to compare three-dimensional scapular kinematics and muscle activity during the ascending phases of both tasks. Individuals with FHRSP displayed significantly greater scapular internal rotation with less serratus anterior activity, during both tasks as well as greater scapular upward rotation, anterior tilting during the flexion task when compared with the ideal posture group. These results provide support for the clinical hypothesis that FHRSP impacts shoulder mechanics independent of shoulder pain

Stiffness and thickness of the upper trapezius muscle increase after repeated climbing bouts in male climbers

Background Indoor climbing involves overloading the shoulder girdle, including the rotator cuff and upper trapezius muscles. This on the field study aimed to investigate the effects of repeated climbing bouts on morphological and mechanical measures of the upper trapezius muscle. Materials and Methods Fifteen experienced male climbers participated in the study. Rate of perceived exertion (RPE), blood lactate concentration ([La−]b), and stiffness and thickness over four points of the upper trapezius were assessed before and after a repeated climbing exercise. The procedure for the climbing exercise consisted of five climbs for a total time of 5-minutes per climb, followed by a 5-minute rest. Results The analysis showed an increase from baseline to after the 3rd climb (p ≤ 0.01) for RPE and after the 5th climb for [La−]b (p ≤ 0.001). Muscle stiffness and thickness increased at all points (1–2–3–4) after the 5th climb (p ≤ 0.01). We found spatial heterogeneity in muscle stiffness and thickness; muscle stiffness was the highest at Point 4 (p ≤ 0.01), while muscle thickness reached the highest values at points 1–2 (both p ≤ 0.01). Moreover, the analysis between the dominant and non-dominant shoulder showed greater stiffness after the 1st climb at Point 1 (p = 0.004) and after the 5th climb at Point 4 (p ≤ 0.001). Conclusions For muscle thickness, the analysis showed significant changes in time and location between the dominant and the non-dominant shoulder. Bilateral increases in upper trapezius muscle stiffness and thickness, with simultaneous increases in RPE and blood lactate in response to consecutive climbs eliciting fatigue

Lumbopelvic Stability During a Single Leg Step Down Predicts Elbow Varus Torque During Baseball Pitching

During a baseball pitch, energy is transferred from the lower extremities through the lumbopelvic junction to produce ball velocity. Reduced lumbopelvic stability has been associated with elbow injury in pitchers, and commonly ulnar collateral ligament (UCL) tears. The primary biomechanical mechanism of UCL tears is high elbow varus torque. Understanding how decreased lumbopelvic stability influences the development of elbow varus torque could identify risk factors of UCL elbow injury. PURPOSE: Characterize the predictive ability of lumbopelvic stability on elbow varus torque during a baseball pitch. METHODS: NCAA Division 1 baseball players (N=44; 19.6+1.3yrs) participated. Pitchers threw ten fastballs from a mound to a catcher over regulation distance. Elbow varus torque was recorded using an inertial measurement unit and ball velocity was recorded with a radar gun. Pitchers also completed a single leg step down (SLSD) task. Triplanar kinematics were recorded for both legs, pelvis and trunk using inertial measurement units. Statistical analysis consisted of a cluster analysis, principal component analysis (PCA), and a multivariate logistic regression model to determine the relationship between lumbopelvic stability and elbow varus torque. RESULTS: Cluster analysis revealed 2 subgroups of pitchers: Low Torque-High Velocity and High Torque-Low Velocity. PCA analysis indicated 4 patterns of SLSD motion variability (principal components): 1-sagittal plane, 2-transverse plane, 3-frontal plane trail limb, and 4-frontal plane lead limb. Increased transverse plane motion of the trunk and pelvis predicted higher odds of belonging to the High Torque-Low Velocity cluster; trunk [Odds Ratio=2.9 (95%CI:1.1,8.0), p=0.036] and pelvis [Odds Ratio=2.6 (95%CI:1.1,6.0), p=0.031]. CONCLUSIONS: Lumbopelvic motion assessed during the SLSD in pitchers can identify deficits that predict high elbow varus torque and low ball velocity during the baseball pitch. Specifically, higher pelvis and trunk transverse plane motion was associated with pitchers in the High Torque-Low Velocity cluster. The SLSD provides an easily accessible method for coaches and clinicians to identify a potential risk factor related to increased elbow varus torque and UCL injury in pitchers

Hip Abduction Strength: Relationship to Trunk and Lower Extremity Motion During A Single-Leg Step-Down Task in Professional Baseball Players

# Background The single-leg step down task (SLSD) is a clinical tool to assess movement and control of the lower extremity and trunk. Hip abduction weakness may impact movement quality during the SLSD, however the relationships between movement and strength are unclear. # Purpose To determine the relationship between hip abduction isometric strength and movement during the SLSD of trunk lean, pelvic drop, knee valgus, and hip flexion. # Study Design Cross sectional, cohort study # Methods One hundred-eighteen Minor League baseball players (age=21.6 ± 2.0 years; n=68 pitchers, n=50 position players) participated. Bilateral hip abduction isometric strength was measured using a handheld dynamometer (HHD), and then multiplied by distance from the greater trochanter to the HHD and expressed as hip abduction torque. Video cameras captured the SLSD, with participants standing on one leg while lowering their contralateral heel to touchdown on the floor from a 0.203m (8in.) step. Trunk lean, trunk flexion, pelvic drop, knee valgus, and hip flexion were measured using Dartfish at heel touchdown. A value of 180° indicated no knee valgus. Pearson correlations examined the relationships between hip abduction torque and SLSD motions. # Results There were no significant correlations for position players. For pitchers, on the lead leg increased hip abduction torque weakly correlated with a decrease in knee valgus (r= 0.24, p=0.049). Also for pitchers on the trail leg, increased hip abduction torque weakly correlated with decreased pelvic drop (r= -0.28, p=0.021). # Conclusion Hip abduction strength contributes to dynamic control of the trunk and legs. Specifically in pitchers, hip abduction weakness was related to increased movement of the lower extremity and lumbopelvic regions during the dynamic SLSD task. These deficits could translate to altered pitching performance and injury. # Levels of Evidence 2\

National Athletic Trainers\u27 Association Position Statement: Evaluation, Management, and Outcomes of and Return-to-Play Criteria for Overhead Athletes With Superior Labral Anterior-Posterior Injuries

Objective: To present recommendations for the diagnosis, management, outcomes, and return to play of athletes with superior labral anterior-posterior (SLAP) injuries. Background: In overhead athletes, SLAP tears are common as either acute or chronic injuries. The clinical guidelines presented here were developed based on a systematic review of the current evidence and the consensus of the writing panel. Clinicians can use these guidelines to inform decision making regarding the diagnosis, acute and long-term conservative and surgical treatment, and expected outcomes of and return-to-play guidelines for athletes with SLAP injuries. Recommendations: Physical examination tests may aid diagnosis; 6 tests are recommended for confirming and 1 test is recommended for ruling out a SLAP lesion. Combinations of tests may be helpful to diagnose SLAP lesions. Clinical trials directly comparing outcomes between surgical and nonoperative management are absent; however, in cohort trials, the reports of function and return-to-sport outcomes are similar for each management approach. Nonoperative management that includes rehabilitation, nonsteroidal anti-inflammatory drugs, and corticosteroid injections is recommended as the first line of treatment. Rehabilitation should address deficits in shoulder internal rotation, total arc of motion, and horizontal-adduction motion, as well as periscapular and glenohumeral muscle strength, endurance, and neuromuscular control. Most researchers have examined the outcomes of surgical management and found high levels of satisfaction and return of shoulder function, but the ability to return to sport varied widely, with 20% to 94% of patients returning to their sport after surgical or nonoperative management. On average, 55% of athletes returned to full participation in prior sports, but overhead athletes had a lower average return of 45%. Additional work is needed to define the criteria for diagnosing and guiding clinical decision making to optimize outcomes and return to play

Risk factors Associated with Shoulder Pain and Disability Across the Lifespan of Competitive Swimmers

Abstract Key Points Competitive swimmers less than 12 years of age had substantial shoulder pain, and older swimmers had pain, dissatisfaction, and disability. High school swimmers were the most symptomatic and incurred the greatest load in terms of hours swum per week and per year. Shoulder pain, dissatisfaction, and disability were correlated positively with increased upper extremity usage in terms of swimming or water polo exposure and were correlated negatively with participation in another sport, specifically soccer for young and running or walking for mature swimmers. Symptomatic swimmers who were less than 12 years of age had reduced shoulder flexibility, weakness of the middle trapezius and shoulder internal rotators, and latissimus dorsi tightness, whereas symptomatic swimmers who were 12 years of age or older had pectoralis minor tightness and decreased core endurance. Because female competitive swimmers have shoulder pain and disability throughout their lives, a program to prevent shoulder injury that might lead to pain and dysfunction is warranted and might include exposure reduction, cross-training, pectoral and posterior shoulder stretching, strengthening, and core endurance training. Each year, millions of people swim for exercise and recreation. Competitive swimmers might practice 5 to 7 days per week and sometimes twice daily. They have shoulder pain at a reported prevalence of 40% to 91%. 1-3 Shoulder pain can be so severe that it leads to functional impairments and termination of participation. A relationship between exposure, which is defined by distance or time spent swimming, and shoulder pain exists, 3 but exposure might not be the only factor related to shoulder pain. Physical impairments found in symptomatic swimmers include reduced shoulder internal rotation strength and external rotation and abduction muscle endurance. Over the past decade, changes have been made in competitive swimming training and equipment, such as more extensive dry-land programs and the use of redesigned paddles to improve stroke mechanics. Given these changes and the high prevalence of pain in swimmers, potentially modifiable physical characteristics of swimmers' exposure and training variables that are related to their pain need to be identified. No researchers have combined training and exposure data with physical examination findings to identify factors related to shoulder pain over an age range from the young team competitor to the master's-level swimmer. Therefore, the purpose of our study was to determine whether physical characteristics, training methods, or exposure differs between swimmers with and without shoulder pain, dissatisfaction with their shoulders, and disability over 4 age groups representing the swimmer's lifespan. Identification of factors that differentiate swimmers with and without shoulder pain could provide the basis for a program to prevent shoulder injury that might lead to pain and dysfunction. Go to: METHODS Participants A total of 236 female swimmers from 8 to 77 years of age volunteered for this multicenter study. Each participant belonged to a youth, high school, or US Masters swim team. Swimmers in the Philadelphia, Pennsylvania, area were invited to participate with their coaches' approval. Adult swimmers and parents or guardians of minors provided written informed consent, and minors signed an assent form. The study was approved by the Arcardia University Institutional Review Board. Procedures Adult swimmers and the parents or guardians of minors completed or assisted with a survey that included demographics, questions about other sport participation, and the amount of participation in swimming on a weekly basis. They also were instructed to indicate the number of months per year they practiced and how many years they had participated in competitive swimming. Shoulder pain and dissatisfaction were assessed using the respective subscales of the Penn Shoulder Score. Next, swimmers rotated through a series of 5 stations where range of motion (ROM), strength, pectoral muscle length, core endurance, and scapular dyskinesis were assessed by members of the research team. This team consisted of an experienced physical therapist (A.T.) and 4 graduate physical therapist students (G.N.T., S.E.K., C.J., A.S.), 2 of whom were certified athletic trainers (G.N.T., S.E.K.). Before data collection on swimmers, 2 training sessions were held in which the research team was given written instructions and practiced the testing procedures. Intrarater reliability of ROM, strength, pectoral muscle length, and scapular dyskinesis was established with 14 athletically active females (age = 23.8 ± 1.7 years). Athletically active was defined as exercising regularly or participating in sports. Intraclass correlation coefficients (ICCs) for continuous data from strength measured by dynamometry, ROM, and pectoral length were fair to excellent (ICC [3,1] = 0.60 to 0.92), and percentage agreement for scapular dyskinesis and manual muscle testing was excellent (κ = 0.83 to 1.0). Station 1: Range of Motion. Passive ROM (PROM) of both shoulders was assessed using an inclinometer for shoulder flexion in neutral rotation with the participant lying supine; shoulder flexion, with the elbow maximally flexed for long head triceps tightness 10 ; shoulder flexion, with the humerus externally rotated, knees and hips flexed, and abdominal muscles actively contracted for latissimus dorsi tightness 10 ; and internal and external rotation, with the shoulder abducted to 90°. Station 2: Strength. Bilateral glenohumeral strength was assessed using a handheld dynamometer (microFET; Hoggan Industries, Draper, UT). For this study, maximal isometric force production was tested for shoulder internal and external rotation with the participant lying prone and the shoulder abducted to 90°; this position has been recommended because swimmers are familiar with it and because it is comfortable and has the highest torque values. 11 Shoulder horizontal abduction strength was measured with the participant lying prone with the elbow extended, and shoulder elevation was measured with the participant standing in the empty-can position (90° of shoulder elevation in the scapular plane and internally rotated). Two repetitions of each test were performed, and an additional repetition was performed if the difference between the first 2 measurements was greater than 1.36 kg. Arm and forearm lengths also were measured and used to calculate normalized torque values, which were obtained by multiplying the dynamometer output by the distance from the shoulder to the application of force and then dividing by body mass. Manual muscle testing was performed bilaterally on the serratus anterior, lower trapezius, and middle trapezius muscles as described by Kendall et al. Station 3: Scapular Dyskinesis. Scapular motion patterns were assessed for winging or dysrhythmia using the scapular dyskinesis test (SDT). The SDT has demonstrated reliability and validity in adult athletes participating in sports that include overhead use of the upper extremity, specifically swimming and water polo. 12,13 Shoulder flexion and abduction each were performed 5 times bilaterally with dumbbells. A 0.45-kg dumbbell was used for participants who weighed less than 36.29 kg, 1.36-kg dumbbells were used for participants who weighed from 36.29 to 68.04 kg, and 2.27-kg dumbbells were used for participants who weighed more than 68.04 kg. These weights were selected based on a pilot study in which Tate et al 14 determined that swimmers could lift the required amount safely. The examiner observed the scapulae from a posterior view and graded the motion pattern as normal or subtle dyskinesis or obvious dyskinesis. Station 4: Endurance. Endurance of core musculature was assessed using the side bridge test Station 5: Pectoralis Minor Length. Pectoralis minor length was measured with a PALM palpation meter (Performance Attainment Associates, St Paul, MN) using surface landmarks validated by Borstad 18 Data Analysis Participants were divided into 4 groups by age, based on the similarity of hours of training and competitive level: ages 8 to 11 years (n = 42), 12 to 14 years (n = 43), 15 to 19 years (high school, n = 84), and 23 to 77 years (masters, n = 67). These groups had different swimming exposures, with respective means of 6.9 ± 2.4, 10.1 ± 4.3, 16.1 ± 6.0, and 4.0 ± 1.7 hours swum per week (P < .001). Cases were classified as positive or negative for substantial pain, dissatisfaction, and disability (PDD) based on the total of the Penn Shoulder Score pain scale and the satisfaction question (range, 0-40, with 40 indicating no pain, fully satisfied) and the total score for swimming disability using the DASH sports module (range, 4-20, with 4 indicating no swimming disability). For the 3 oldest groups (age > 11 years), a positive case (+PDD) had to meet 2 criteria: (1) The DASH sports module score was greater than 6 points and (2) the Penn Shoulder Score was less than 35 points. For the DASH sports module, a score greater than 6 points requires the swimmer to have at least mild difficulty in 3 of the 4 areas (difficulty with usual technique, swimming because of pain, swimming as well as she would like, and spending usual amount of time practicing swimming) or moderate or severe difficulty or inability in at least 1 of the 4 areas. A Penn Shoulder Score of less than 35 points for pain and satisfaction reflects change greater than 5 points, which exceeds the total error (standard error of the mean) for the combined pain and satisfaction sub-scales. 8 All cases not satisfying the requirements for +PDDs were classified as −PDDs. In the youngest group (age range, 8-11 years), only 1 of 42 swimmers fit the +PDD definition used for the older participants, which precluded further data analysis. Therefore, in the 8-to 11-year-old age group, a case was considered positive if the swimmer rated her pain equal to or greater than 2 of 10 with strenuous activity on the Penn Shoulder Score pain scale. All cases that did not satisfy the requirements for +PDDs were classified as −PDDs. For swimmers with bilateral symptoms, the data from the most painful side were used for +PDDs. For swimmers with equal pain bilaterally or no pain, the participants were listed in consecutive numeric order based on age, and alternate sides were selected. Continuous variables for participant demographics, exposure, and physical examination were compared using independent t tests. Categorical variables were compared using χ 2 tests. When we found categorical variables in which 20% of the cells did not contain a minimum of 5 cases and therefore did not meet the assumption of expected cell frequency, we used a Fisher exact probability test. A 1-tailed test was used for the variables we hypothesized had a directional preference based on pilot data: history of traumatic injury, unilateral breathing pattern, and participation in water polo. 14 A 2-tailed test was used for all other variables. To determine whether stroke specialty (butterfly, backstroke, breaststroke, or freestyle) was associated with pain and disability, the data from all age groups were combined because a failure to meet minimum cell count for χ 2 occurred within each age group. We used SPSS (SPSS Inc, Chicago, IL) for data analysis. Go to: RESULTS The number of +PDDs was 9 of 42 (21.4%) in swimmers aged 8 to 11 years, 8 of 43 (18.6%) in swimmers aged 12 to 14 years, 19 of 84 (22.6%) in high school swimmers, and 13 of 67 (19.4%) in masters swimmers. Participant demographics for +PDDs and −PDDs are presented in DISCUSSION Competitive swimmers are at risk for developing shoulder pain and disability, which can lead to dissatisfaction with the use of their shoulders during swimming and daily activities. Although specific differences in swimmers with and without symptoms have been investigated extensively, we are the first to our knowledge to collectively use validated and reliable methods to test groups of swimmers poolside without expensive, labor-intensive equipment. This method has allowed us to assess physical performance and exposure variables in competitive swimmers aged 8 to 77 years and to document the presence of shoulder symptoms throughout the lifespan of swimmers. Potential factors related to shoulder pain and disability are exposure time to swimming, training methods, and physical characteristics of the swimmers. We found that 18.6% to 22.6% of competitive swimmers in each of our 4 age groups experienced shoulder pain and disability. Swimmers less than 12 years of age primarily had pain, whereas participants more than 12 years of age experienced pain, dissatisfaction, and disability with the use of their shoulders. The high school swimmers were the most symptomatic. Factors related to shoulder pain, dissatisfaction, and disability with shoulder use in 2 or more age groups were greater swimming exposure, a history of traumatic shoulder injury, participant-rated feeling of instability, and reduced participation in another sport or activity (cross-training). Additional factors associated with symptoms in only a single age group were less shoulder flexion ROM, less strength of shoulder internal rotation and the middle trapezius, shorter pectoralis minor, latissimus dorsi tightness, more participation in water polo, bilateral breathing, and less core endurance. We found significant differences between participants with and without shoulder pain, disability, and dissatisfaction in exposure and physical characteristics but found no differences in age, height, mass, or body mass index. For all age groups, the +PDD group had greater exposure than the −PDD group in terms of years swum and of hours per week and hours per year practiced; however, we found differences in exposure only in the high school and masters groups. High school swimmers in the +PDD group had 1.50 ± 1.14 years more swimming exposure than those in the −PDD group. In a study of elite competitive swimmers aged 13 to 25 years, Sein et al 3 found a correlation between years of training and supraspinatus tendon thickness on magnetic resonance imaging. They reported that all swimmers with tendon thickening had supraspinatus tendinopathy and shoulder impingement pain. In our study, both +PDD and −PDD swimmers averaged more than 15 hours per week of swimming, and some swimmers reported swimming 10 000 m or more daily. Sein et al 3 also found that athletes who swam more than 15 hours per week were twice as likely to have tendinopathy as those who trained less. This might help explain our finding that high school athletes had the highest levels of pain and disability. Allegrucci et al 2 estimated that competitive swimmers performing 10 stroke cycles per 25 m and covering 10 000 m per day would incur 4000 shoulder revolutions daily. Given that repetitive upper extremity usage at or above shoulder level has been identified as a risk factor for shoulder pain, it is not surprising that those with greater exposure have pain and disability. In the masters group, the +PDD group swam a greater number of hours per year (223.60 ± 81.81 hours) than the −PDD group (163.88 ± 81.22 hours), and a trend was seen for hours swum per week. The association between exposure and pain and disability in our study is consistent with that reported in other studies, in which the presence of supraspinatus tendinopathy in elite swimmers was predicted 85% of the time from hours swum per week alone or in combination with distance swum per week. 3 Although pitch-count rules exist for youth baseball pitchers, no exposure recommendations are available to guide coaches of youth competitive swimmers. Whereas increased swimming exposure and participation in water polo were positively associated with pain and disability, other findings had a negative association. Specifically, the 8-to 11-year-old −PDD swimmers more frequently participated in another sport, with soccer specifically reported, and the −PDD masters swimmers more frequently participated in a walking or running program than their symptomatic counterparts. Independent t tests revealed no difference in the amount of time spent swimming in terms of hours per week, hours per year, or years of participation between the groups that did and did not participate in these activities. Although we cannot conclude that participation in other activities offers a direct protective mechanism, these findings lend support to the concept of cross-training. Investigators of the effects of cross-training have concluded that adolescents participating in several sport and exercise activities throughout the year were less likely to experience neck, shoulder, or low back pain. Whereas Richardson and colleagues 23 found that unilateral breathing patterns increased the risk of shoulder problems, we found that the 8-to 11-year-old +PDD group had a greater incidence of a bilateral breathing pattern. Young swimmers may lack appropriate stroke mechanics, but this cannot be determined from our study. Although a trend existed for the +PDD group to breathe unilaterally at the high school level, we found no differences in breathing patterns among the other 3 age groups. A history of a traumatic injury to the shoulder, such as a dislocation, fracture, or fall, was reported more frequently in the +PDD group in swimmers from 3 groups (age 12 years through masters). These injuries may have left residual deficits that pre-disposed them to pain and disability. Similarly, +PDD swimmers in the 12-to 14-year-old and high school groups more frequently answered "yes" when asked, "Does your shoulder feel unstable, or do you feel like it ever 'slips' out of place?" These findings suggest that swimmers with previous injuries or instability should be assessed to determine whether they have deficiencies that could be addressed to reduce the risk of shoulder pain. Although paddle use has been associated with pain, 23 our data did not show differences in swim paddle use between +PDD and −PDD groups. Paddle design has changed from solid and rectangular to a shape that conforms to the hand and is perforated to reduce resistance. In addition, coaches might be more judicious in their use of paddles because of findings reported in previous studies. Individual stroke preference was not found to differ between +PDDs and −PDDs. This finding is consistent with that of Sein et al, 3 who reported that strokes have little effect on predisposition to shoulder pain. This is not surprising because practice sessions typically involve 80% freestyle swimming. 7 Core endurance measured by time held for the side bridge position was less (8.5 seconds) in the 12-to 14-year-old +PDD group. Trends of reduced core endurance were seen for the high school and masters-level swimmers. The side and prone bridge positions evoke increased activity in the external oblique abdominis and the rectus abdominis in addition to requiring glenohumeral and scapular control. Scapular winging due to trapezius or serratus anterior fatigue would result in test termination due to loss of core position. High levels of serratus anterior muscle activity have been demonstrated for the forearm push-up plus, 24 which is essentially an isometric hold of the prone bridge exercise. Fatigue of the shoulder and trunk musculature might initiate the development of pain in the swimmer's shoulder, Reduced resting length of the pectoralis minor was found in the high school +PDD group, and a trend was seen in the youngest swimmers. People with shorter pectoralis minor muscles have displayed altered scapular kinematics, with less scapular posterior tilting and greater internal rotation during humeral elevation. Reduced posterior shoulder flexibility assessed with internal rotation PROM at 90° of abduction was found in the 8-to 11-year-old +PDD swimmers. Harryman et al 28 noted that selective tightening of the posterior capsule produced superior and anterior humeral head translation. This could reduce subacromial space during overhead upper extremity use and cause shoulder pain due to impingement. Three-dimensional videography has supported this finding by showing that people with limited shoulder internal rotation were likely to experience a large amount of mechanical impingement during the swimming stroke. 29 The 8-to 11-year-old swimmers with pain also had reduced flexion ROM with latissimus dorsi tightness. Reduced flexion ROM, which we tested with the shoulder in neutral rotation, might be attributed to capsular tightness, but reduced flexion with the pelvis posteriorly tilted and shoulder externally rotated is proposed to be due to tightness of the latissimus dorsi. If one chose to implement a stretching program to address limitations in shoulder elevation, a differentiation should be made about the restricted structure so that specific stretching exercises could be given. Theoretically, swimmers with reduced flexion ROM could have a reduced stroke length and, therefore, need additional strokes compared with swimmers with greater mobility, incurring greater shoulder load. However, because older swimmers exhibit shoulder hypermobility 7 and stretching has been reported to aggravate shoulder symptoms, 1 careful consideration should be given when evaluating potential merits of shoulder elevation stretching. Consistent with findings reported in previous studies, 6,7 none of the other age groups showed a difference in flexion ROM between swimmers with and without PDD. The frequency of obvious scapular dyskinesis was not different between the +PDD and −PDD groups in any age group. This differs from findings reported by Bak and Magnusso