Effect of Stretching and Strengthening Shoulder Muscles on

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Shoulder Posture in Competitive Swimmers 59

J Sport Rehabil. 2006, 15, 58-70© 2006 Human Kinetics, Inc.

The authors are with the Dept of Rehabilitation Sciences, University of Kentucky, Lexington, KY 40536-0200..

Effect of Stretching and Strengthening Shoulder Muscles on Forward Shoulder

Posture in Competitive Swimmers

Mark Kluemper, Tim Uhl, and Heath Hazelrigg

Context: Imbalanced shoulder muscles might cause poor posture in swimmers, which has been implicated as potential cause of injury. Objective: To determine whether a training program can reduce forward shoulder posture. Design: Pro-spective pseudorandomized. Setting: College swimming pool. Participants: 39 competitive swimmers (age 16 ± 2 years) divided into an exercise group (n = 24) and a control group (n = 15). Intervention: The experimental group performed a partner-stretching program on the anterior shoulder muscles and a strengthening regimen focusing on the posterior shoulder muscles for 6 weeks. The control group participated in normal swim-training activities. Main Outcome Measures: Shoulder posture was measured as the distance from the anterior acromion to a wall using a double-square method. Results: The experimental group significantly reduced the distance of the acromion from the wall in a resting posture (–9.6 ± 7.3 mm) as compared with the control group (–2.0 ± 6.9 mm). Conclusions: A training routine might reduce the forward shoulder posture present in most competitive swimmers. Key Words:

The biomechanics of competitive swimming are such that the shoulderʼs internal rotator and adductor muscles become stronger and hypertrophied relative to antagonist muscles.1 Previous authors have suggested that this strength imbal-ance of the anterior shoulder muscles can pull the shoulder forward, producing a protracted posture. This forward shoulder and protracted scapula have been associ-ated with painful shoulders in swimmers.2 An MRI investigation on a small sample showed that the subacromial space decreases with protraction.3 In addition, Pink and Tibone4 have suggested that a protracted shoulder posture might predispose swimmers to a high risk of shoulder injury.

The shoulder is a vulnerable joint in competitive swimmers.5 A number of studies have been performed to identify the incidence of shoulder problems in swimmers, and a wide range of results have been reported, from a low of 3% to a high of 80%.6-8 This surprisingly wide range of results is partly a result of the lack of a precise description of “shoulder problems” in the surveys. One author defined

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Shoulder Posture in Competitive Swimmers 59

significant shoulder pain as pain that interferes with training or progress in training and reported that 35% of elite-level swimmers suffered from this type of pain.5 It has also been reported that 90% of all complaints by swimmers of a magnitude necessary to seek advice from a physician are shoulder related.8

In most other sports, the foot or feet must be planted on the ground in order to initiate a propulsive ground-reaction force. There is no such force in swimming. Up to 90% of the propulsive force in competitive swimming comes from the upper extremities.4 Another unique feature of swimming is the demand for upper extrem-ity endurance. Competitive swimmers might swim 10,000 to 14,000 m/day, 6 or 7 days/wk. This distance equates to approximately 2500 strokes of the shoulder joint per day.4 In fact, it has been estimated that the average college swimmer per-forms more than 1 million strokes annually with each arm.8 This information leads many to conclude that most shoulder injuries in swimmers result from overuse.9,10 Although repetition is certainly a factor in the development of shoulder pain, the fact that not all high-yardage swimmers develop pain suggests that overuse must be combined with other contributing factors.8 Several factors, such as muscle strength, musculotendinous flexibility, joint laxity, and posture, might contribute to shoulder injuries and pain. These factors are interrelated, and it is often difficult to determine specific cause and effect.

In 3 of the 4 strokes in competitive swimming (freestyle, butterfly, and back-stroke) the upper body force needed to move the swimmer through the water comes primarily from adduction and internal rotation of the shoulder, which leads to an agonist–antagonist muscle imbalance.1,11 An analysis of shoulder muscles in competitive swimmers found an adduction-to-abduction strength ratio of 2.05:1 (compared with 1.53:1 in nonswimmers) and an internal-rotation-to-external-rota-tion strength ratio of 1.89:1 (1.35:1 in nonswimmers).4 These muscle adaptations are consequent to the training effect of swimming. Fine-wire electromyography testing has shown that the supraspinatus and infraspinatus play only a minor role during the swimming stroke, whereas the major propulsive forces are generated by the shoulder adductors and internal rotators.12 In highly trained athletes an adapta-tion of increased activation of agonist over antagonist muscles has been reported in both upper and lower extremity athletes.13,14 As a result of these neuromuscular and strength adaptations the commonly observed forward head and rounded shoulders in swimmers might develop over time.2,4,15 Possibly this phenomenon is caused by the stronger internal rotator and adductor muscles pulling the clavicle and scapula forward, over the weaker external rotator and abductor muscles.4

Patients with shoulder impingement demonstrate diminished posterior tilt-ing of the scapula during humeral elevation, a factor that decreases subacromial space.16,17 It appears reasonable that stronger anterior muscles, particularly the pectoralis minor, might have a critical role in this phenomenon. It is suggested by Kendall et al18 and Sahrmann19 that stretching the tight muscles and strengthening the antagonistic muscles is the appropriate intervention for correcting this positional or postural fault caused by muscle imbalance. If this forward shoulder posture can be addressed through a program of stretching and strengthening, perhaps the risk of shoulder injury can be reduced. The purpose of this study was to determine whether a functional 6-week stretching and strengthening program could reduce forward shoulder posture in young, elite-level competitive swimmers.

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60 Kluemper, Uhl, and Hazelrigg Shoulder Posture in Competitive Swimmers 61

Methods

Design

This study employed a prospective pseudorandomized pretest–posttest design. The dependent measure of shoulder posture was measured with a double square. With the subject standing against a wall, the distance between the anterior acromion and the wall was measured bilaterally. Measurements were taken in 2 positions, resting and an “upright military” posture before and after a 6-week time interval. Participants were assigned to a group, the independent variable. The exercise group participated in a stretching and strengthening program along with their normal swim training while the control group carried out their normal swim-training program.

Subjects

The study group comprised 39 (14 male and 25 female) elite-level, high-school- and college-age competitive swimmers from 2 swim teams. Team A (24 members: 10 male, 14 female; age 16 ± 2 years) was designated as the experimental group, and Team B (15 members: 4 men, 11 women; age 16 ± 1 years) acted as the control group. This all-inclusive team division was done at the request of both coaches (see the “Limitations” section).

Subjects were included in this study if they had no current limitations in swimming and dry-land training as a result of shoulder pain. All subjects signed an informed consent approved by the universityʼs institutional review board (IRB) before participation. Parents or legal guardians of all subjects under 18 years of age also signed the consent form. In addition, all subjects under 18 signed an assent form approved by the universityʼs IRB.

Testing Procedure

Measurements of both the right and left shoulder of each subject were taken before and after a 6-week stretching and strengthening program. A device known as the double square (Model #420EM, Johnson Level and Tool Manufacturing, Inc, Mequon, Wisc) was used to quantify forward shoulder posture.15 The double square consists of a 40-cm combination square with a second square/level added in an inverted position (Figure 1). This device was used to measure the distance (in millimeters) from the wall to the anterior tip of the subjectʼs acromion process. After palpating the anterior tip of the acromion process on the subjectʼs left and right shoulder, the location was marked on the subjectʼs skin with a permanent marker. The subject was then instructed to place his or her heels against the wall and was verbally instructed to “assume an upright, military posture.” At this point the double square was positioned over the subjectʼs left shoulder with 1 square flush against the wall. The second square was adjusted until it touched the marked tip of the subjectʼs left acromion. Three measurements were taken and recorded. The exact measurement process was repeated on the subjectʼs right shoulder. The subject was then instructed to relax into his or her normal posture. At this point the entire measurement process was repeated. The military posture was incorporated in order to ensure that participants would not inadvertently alter their relaxed normal posture during the measurement process.

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The mean of the 3 posture measurements was used for statistical analysis. For all subjects in both groups, measurements were taken with the same equipment and by the same investigator throughout the study to ensure accuracy and identical instructions. All measurements were conducted during a morning swim practice, at the same location against the wall.

A pilot study was conducted to ascertain the intrarater reliability of the double-square measuring device. All of the same procedures of measurement with the double square were conducted on 4 subjects, twice by the same investigator, with a 4-day interval between measurements. The 2 measurements were compared to calculate the intraclass correlation coefficient (ICC2,1). Measurements on the right and left shoulders were found to be very reliable, with ICC values of .99 and an SEM of 0.1 mm for both sides. A previous study using the same procedures also reported high intrarater reliability for the double-square method, with an ICC value of .89.15

Exercise Procedure

After the initial shoulder measurements were recorded, the subjects in the experi-mental group began a 6-week stretching and strengthening program. The exercises were conducted 3 times per week during the subjects ̓scheduled morning swim-team practice. At each practice the swimmers warmed up in the pool for 20 to 30

Figure 1 — Double-square method used to measure forward shoulder posture.

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minutes before performing the exercise routine. A time restriction of 15 minutes for the exercise routine was required to minimize interference of swim practice at the coaches ̓request. After the exercise routine the subjects completed their swim practice. At the first session, the subjects were introduced to the different levels of Theraband® exercise bands (Hygenic Corp, Akron, Ohio). These bands are color-coded, with each color representing a different resistance. The investigators then demonstrated and described the nature of each strengthening exercise (Table 1, Figures 2–4). All of the subjects had previous experience with strength training as part of their usual workout routine. The subjects were given the opportunity to do 5 repetitions of each exercise with several levels of Theraband in order to estimate which level was appropriate for themselves. While these test exercises were being conducted, the investigators evaluated the subjects for proper technique. The subjects then carried out the prescribed protocol for the first week of strength training: 3 sets of 10 repetitions of all strengthening exercises.

After the exercises, the subjects were asked if the tubing they had chosen was too challenging (they were not able to complete the full 3 sets or could not finish while maintaining proper technique), appropriately challenging (the final 3 or 4 repetitions were a struggle, but they were able to maintain proper technique), or not challenging enough (repetitions were completed with little or no struggle). On the basis of this feedback and the investigators ̓technique analysis, some of the subjects were assigned a different level of exercise band. If a subject reported

Table 1 Description of Theraband® Latex-Band Resistance Exercises Used During the 6-Week Training Program

Exercise Description

Scapular retraction With the shoulder abducted to 90° in the scapular plane, the elbows flexed to 90°, and the forearms horizontal, the subject holds a section of the exercise band between the right and left hands and the scapulae are retracted, stretching the band (Figure 2). The subject must maintain the original 90° position of the shoulders and elbows and then execute a controlled return to the starting position.

External rotation The upper arm is positioned at 90° of shoulder abduction and 90° of elbow flexion. The forearm begins in a horizontal position and externally rotates into a vertical position. The subject then executes a controlled return to the starting position. The exercise band is fixed in front of the subject at approximately waist height at the beginning of the exercise (Figure 3).

Shoulder flexion for the lower trapezius

With arms flexed to 90°, elbows fully extended, and palms down, the subject flexes the shoulders to 180° against the exercise-band resistance and then executes a controlled return to the starting position. The exercise band is again fixed in front of the subject at approximately waist height for the beginning of this exercise (Figure 4).

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Figure 2 — Scapular-retraction strengthening exercise with Theraband® latex bands for resistance. (a) Exercise starting position and (b) exercise finish position. (See Table 1 for a full description of this exercise.)

(a) (b)

(a) (b)

Figure 3 — External-rotation strengthening exercise with Theraband® latex bands for resistance. (a) Exercise starting position and (b) exercise finish position. (See Table 1 for a full description of this exercise.)

a level as too challenging, the next lower level of the exercise band was used; if a level was not challenging enough, the next higher level was used for the next exercise session. The exercise progression, depicted in Table 2, was based on the work of Wang et al20 in which a similar protocol produced significant strength gains. The subjects were then given the opportunity to ask any questions about the strengthening exercises, after which they were asked to pair up with a partner of similar height and build.

The investigators then demonstrated and described the nature of each stretching exercise (Figures 5 and 6). The first stretch, for anterior chest muscles, required the subject to assume a supine position on a 5-in-diameter foam roll, which runs

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Figure 4 — Shoulder-flexion strengthening exercises, emphasizing the lower trapezius muscle fibers. (a) Exercise starting position and (b) exercise finish position. (See Table 1 for a full description of this exercise.)

(a) (b)

Table 2 Progression of the Exercises

Week 1 Week 2 Week 3 Week 4 Week 5 Week 6

Repetitions 3 × 10 3 × 15 3 × 20* 3 × 10 3 × 15 3 × 20*At the end of the third week the subjects progressed to the next higher level of resistance using the Theraband® latex band.

down the center of the back. The subjectʼs partner grasps the subjectʼs shoulders and slowly presses them down in the direction of the floor until instructed to stop and hold for 30 seconds. This was repeated twice per training session (Figure 5). The second stretch for shoulder internal rotators required the subject to assume a kneeling position in front of his or her standing partner and lace his or her fingers behind the head. The partner then reaches in front of the subjects ̓arms and back behind the subjectʼs scapulae, lacing his or her fingers together, as well. The part-ner pulls in a diagonal direction, both up and back from the subjectʼs trunk, until instructed to stop and hold by the subject (Figure 6). The stretch was held for 30 seconds and repeated twice per training session.

The subjects worked with their partners to carry out the stretching exercises. The investigators evaluated subjects ̓performance for proper technique. At least 1 investigator and 1 coach were present at all exercise sessions for supervision and ongoing technique evaluation for the entire 6 weeks.

Statistical Analysis

The change in forward-shoulder posture measurement with the double square was calculated (posttest score – pretest score = difference) for both shoulders in each

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Figure 6 — Stretching the pectoralis major.

Figure 5 — Stretching the pectoralis minor.

test position. To determine the effectiveness of the intervention, the difference score was used to compare the 2 groups. A mixed-model, repeated-measures ANOVA with 1 within factor (side) and 1 between factor (group) with an alpha level set at P ≤ .05 was performed for each test position separately.

Results

The descriptive statistics demonstrating the difference between the pretest and posttest measurements for each shoulder and test position are presented in Table 3. There were no significant interactions between group and side in either test position. There was a significant main effect for group in the relaxed-posture test

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position (F1,37 = 11.4, P < .01). The experimental group decreased their forward posture significantly more than the control group (–9.6 ± 7.3 mm vs –2.0 ± 6.9 mm, respectively.).

Comments

The incidence of swimmerʼs shoulder is quite high in competitive swimmers, and several factors including lack of shoulder flexibility, muscle imbalance, endurance, and posture might contribute to it.7 The focus of this research was to examine posture to determine whether a 6-week intervention program could have a positive effect on static shoulder posture. The subjects in this study were all swimmers involved with a year-round competitive swim team. All had some degree of the forward shoulder posture that is typical of competitive swimmers. Studies have shown that 35% of swimmers at this training level report shoulder pain.5 Some of the subjects in this study reported having had shoulder pain in the past, but none were currently experiencing pain to the extent that it prevented them from participating in a full training schedule. The current study revealed that the swimmers who participated in the 6-week stretching and strengthening program had more of an upright posture, with the acromion process closer to the wall in postexercise testing. Based on these results, we think that the exercise regimen chosen for this study was appropriate to improve posture. The variability of the change might be accounted for by dif-ferences in height—a change of 25% in tall and short individuals will result in different linear change because of the differences in the lengths of their clavicles. In addition, subjects with good posture initially did not change much, and others with poor posture might have changed a large amount.

Earlier work with a different population, using a different series of strengthen-ing exercises, showed an increase in strength but could not support the use of the exercises to alter shoulder posture.20 Studying an organized swim team and having them perform strengthening and stretching program under direct supervision might

Table 3 Difference in Pretest and Posttest Scores (mm) for Both Groups Measured in Both Test Positions

ControlGroup

Experimental Group

Mean SD Mean SD

Upright military postureright 0.6 2.7 –0.9 3.7left –0.20 3.3 –2.2 8.9

Relaxed posture*right –4.20 13.30 –9.4 7.7left 0.2 2.4 –9.8 7.5

*Significantly (P < .05) greater change in posture in the relaxed test position for the experimental group over the control group.

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account for some of the results found in this study. Coaches of competitive swim programs have been taught for years that strengthening posterior muscle mass of the shoulder is a key to preventing shoulder injuries. As a result, most swim teams include strengthening exercises that target the same muscles that we addressed in this study into their dry-land exercise program. A recently published study con-cluded that swimmers who participated in a functional strength-training program had a significantly lower incidence of shoulder pain than did those in the control group.21 Several of the exercises performed in the present study were similar to those in the program cited in that study. Therefore, strength training appears to be a positive element in injury prevention.

We think that the supervised stretching program contributed to the positive findings of this study. Combining stretching of the hypertrophied anterior shoul-der muscles with strengthening of the relatively weaker posterior muscles might have a significant synergistic effect on shoulder posture. A stretching program that requires a 30-second hold and repeats each exercise 2 times has been demonstrated to increase muscle length in the hamstrings.22 Perhaps this focused stretching rou-tine, aimed at lengthening the shoulderʼs internal rotator and adductor muscles, combined with the strengthening exercises was important to effect the postural changes that were found in this study but not in previous studies.

Another key factor that might account for the positive results in this study is subject compliance. At least 1 investigator and at least 1 coach supervised each exercise session. In addition, both teams that participated in this study have strict attendance requirements. For both groups, the overall attendance for subjects par-ticipating in the study was reported by the coaches to be 87% for the experimental group (Team A) and 89% for the control group (Team B). This high level of compli-ance enabled the investigators and coaches to monitor stretching and strengthening technique and effort closely. In the event of a missed session, the coach required the subject to make up the exercise program at either the evening practice on the same day or at the practice session on the following morning. In the study by Wang et al,16\ the subjects did their exercises as part of a home-exercise program and were monitored through weekly telephone contact. The close monitoring at every session in the present study enhanced the productivity of the exercises by enabling the quick correction of errors and lapses in concentration.

Limitations

As in all studies, limitations arise that can affect final results. In order to recruit the number of subjects necessary for this study, swimmers on 2 teams were invited to participate. Ideally, a true random sampling would have been used for the com-position of the experimental and control groups, but this was not a popular option with the coach of either team. Both coaches agreed to allow their swimmers to participate only if all members of each team acted as either the control group only or the experimental group only. Accordingly, a pseudorandom sample of conve-nience was used for this study.

Both coaches have very similar philosophies of training and had actually coached on the same team in the past. Swimming yardage totals were also very similar over the span of the 6-week study. The members of the control group

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swam an average of 49,974 m/wk, and the experimental group swam an average of 51,966 m/wk. It cannot be determined, however, whether the subtle differences of the workouts of the 2 teams had any bearing on the results.

In the preexercise testing, measurements of both right and left shoulders of the experimental group were considerably larger those of the control group. It is not clear why this was so. A review of the subject pool during statistical analysis revealed that 73% of the control-group population was female versus 58% of the experimental group. It seems reasonable that a larger male frame could result in a larger measurement in most cases. This was not intentional, and we would recom-mend a more even distribution of male and female subjects in future studies.

A review of the literature revealed no definitive, evidence-based method of measuring shoulder posture. Peterson et al15 investigated the validity and reliability of 4 methods of measuring forward shoulder posture. They used a comparison with lateral radiographs to determine validity. The double-square method used in this study was one of the methods used by Peterson et al. Although they could not support the validity of any of the 4 methods, all were found to have high intrarater reliability. In addition, they concluded that the double-square method “was accu-rate in detecting changes in a patientʼs shoulder posture, and would be of clinical value for this purpose.”15(p The double-square method used in this study had high intrarater reliability, but several variables still exist. One factor that might have an effect in this case is the subjects ̓ability to assume a normal posture while standing with heels against the wall. Perhaps the proprioceptive input from the wall altered the subjects ̓posture. Peterson et al expressed a concern about this, as well. An attempt to account for this factor was the use of a military posture initially. This created a reference for the subjects of maximal upright posture and yielded values on average 25 mm less than resting-posture values, indicating that resting values approximated a true relaxed posture. This upright military posture was found not to change significantly throughout the study for either group, supporting the fact that this posture served as a consistent reference for subjects.

Another potential factor might be the subjects ̓desire to show improvement. Observations have found that simply mentioning posture to a group of subjects results in many people standing or sitting more upright. Did the subjects ̓desire to improve therefore lead them to consciously or unconsciously stand more upright during posttesting? There is no way to determine whether these issues played any role in the results from this study.

Previous research involving shoulder measurements to evaluate posture typi-cally evaluated only 1 shoulder on each subject, usually the right shoulder.15,20,23 We conducted measurements of both shoulders in our study. The process revealed interesting data demonstrating that the mean distance from the wall to the anterior border of the acromion process was greater on the right shoulder than on the left. This was true with both teams at both preexercise measurements and postexercise measurements. Perhaps this is related to hand dominance, because 36 of the 39 subjects indicated that they were right-handed. Although no literature could be found to address this specific aspect of shoulder posture, the general relationship between hand preference and posture has been studied. Raine and Twomey24 con-cluded that, despite the suggestion that there is a relationship between unevenness of the shoulders and handedness, their results did not strongly support the belief that hand preference and shoulder height in the coronal plane are related. They also

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found no association between hand preference and coronal shoulder angle (forward shoulder posture). Their subjects were a random population of men and women who were not swimmers or athletes, so perhaps hand dominance and its relationship to swimming-stroke patterns has some bearing on the findings.

Future Studies

The positive trend in these results is encouraging and shows evidence of the need for further studies. Incorporating a larger subject pool and a third group performing only 1 of the exercise programs might shed further light on the effect of stretching on static shoulder posture. A season-long study might further confirm the findings of this research. In addition, a study to determine whether the swimmers performing these exercises experience fewer cases of shoulder pain or greater improvement in the pool would shed light on the need for an exercise protocol of this type. After all, if the decrease in forward shoulder posture does not lead to a functional benefit, the stretching and strengthening program would not be warranted.

Conclusions

The results of a 6-week training program indicate that stretching anterior shoulder soft tissue, primarily the internal rotator and adductor muscle groups, and strength-ening posterior shoulder muscles, including the external rotator and abductor groups, can reduce forward shoulder posture in competitive swimmers. In addition, dif-ferences between right- and left-shoulder posture were identified, demonstrating the importance of measuring both shoulders in future research. Because posture, muscle imbalance, and joint laxity have been shown to contribute to the incidence of shoulder problems, a stretching and strengthening program such as the one performed in this study might be a beneficial addition to competitive swimmers ̓year-round dry-land training program.

Acknowledgments

We owe a debt of gratitude to Phil Page, MS, PT, ATC, coordinator of clinical research at the Theraband Academy, and to the Theraband Academy for providing the Theraband latex bands necessary for this study. Authors Mark Kluemper and Heath Hazelrigg performed this study as part of their educational preparation in physical therapy at the University of Kentucky.

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Effect of Stretching and Strengthening Shoulder Muscles on