Investigation of scapulohumeral rhythm, range of motion and strength in elite swimmers with and without scapular dyskinesis

Investigation of scapulohumeral rhythm, range of motion and strength in elite swimmers with and without scapular dyskinesis

FARZAD SAEEDIYOUN1, ALI ASGHAR NORASTEH2, LEILA YOUZBASHI3

1Department of Corrective Exercises and Sport Injuries, Faculty of Sport Sciences, University of Guilan, Rasht, Iran; 2Physiotherapy Department, Faculty of Medicine, Guilan University of Medical Sciences, Rasht, Iran; 3Department of Sport Science, Faculty of Humanities, University of Zanjan, Iran.

Summary. Background. Changes in the normal position of the scapula and the function of its stabilizing muscles can be a significant factor in creating abnormal shoulder girdle biomechanics. The strength and range of motion of the shoulder girdle and the scapulohumeral rhythm have been identified as contributing factors to scapular dyskinesis in individuals with scapular dyskinesis. The aim of the present study is to investigate the scapulohumeral rhythm, dyskinesis, as well as strength and range of motion in elite swimmers. Methods. This research is a causal-comparative. A total of 40 elite swimmers purposefully selected and divided into two groups of 20 individuals with (age: 19.13 ± 2.32 years) and without (age: 20.00 ± 2.95 years) scapular dyskinesis based on inclusion criteria. Results. There were no significant differences in the scapulohumeral rhythm at the 45-degree angle (p=0.998), 90-degree angle (p=0.999), and 135-degree angle (p=0.156); in the isometric strength for shoulder flexion (p=0.556), extension (p=0.671), abduction (p=0.648), internal rotation (p=0.521), external rotation (p=0.621), scaption (p=0.704), scapular elevation (p=0.858), and scapular protraction (p=0.899); in the range of motion for shoulder flexion (p=0.637), adduction (p=0.312), abduction (p=0.283), internal rotation (p=0.829), and external rotation (p=0.291). However, there was a significant difference in the isometric strength for shoulder adduction (p=0.048); in the range of motion for shoulder extension (p=0.004). Conclusion. So, it is advisable to consider exercises to increase the range of motion for swimmers with scapular dyskinesis. Scapular dyskinesis may lead to an increase in shoulder adduction strength in swimmers.

Key words. Dyskinesia, isometric strength, overhead athletes, range of movement.

Indagine sul ritmo scapolo-omerale, sull’ampiezza del movimento e sulla forza nei nuotatori d’élite con e senza discinesia scapolare

Riassunto. Background. Le alterazioni nella posizione normale della scapola e nella funzione dei muscoli stabilizzatori possono rappresentare un fattore significativo nell’alterazione della biomeccanica del cingolo scapolare. La forza e il range di movimento del cingolo scapolare, così come il ritmo scapolo-omerale, sono stati identificati come fattori che contribuiscono alla disfunzione scapolare nei soggetti con discinesia scapolare. Scopo del presente studio è indagare il ritmo scapolo-omerale, la discinesia, la forza e il range di movimento nei nuotatori d’élite. Metodi. Questa ricerca ha un disegno causale-comparativo. Sono stati selezionati intenzionalmente 40 nuotatori d’élite, suddivisi in due gruppi da 20 soggetti ciascuno, con (età: 19,13 ± 2,32 anni) e senza (età: 20,00 ± 2,95 anni) discinesia scapolare, secondo criteri di inclusione prestabiliti. Risultati. Non sono state riscontrate differenze significative nel ritmo scapolo-omerale agli angoli di 45 gradi (p=0,998), 90 gradi (p=0,999) e 135 gradi (p=0,156); nella forza isometrica per la flessione (p=0,556), estensione (p=0,671), abduzione (p=0,648), rotazione interna (p=0,521), rotazione esterna (p=0,621), scaption (p=0,704), elevazione scapolare (p=0,858) e protrazione scapolare (p=0,899); nel range di movimento per flessione (p=0,637), adduzione (p=0,312), abduzione (p=0,283), rotazione interna (p=0,829) e rotazione esterna (p=0,291) della spalla. Tuttavia, è emersa una differenza significativa nella forza isometrica per l’adduzione della spalla (p=0,048) e nel range di movimento per l’estensione della spalla (p=0,004). Conclusioni. È quindi consigliabile includere esercizi specifici per aumentare il range di movimento nei nuotatori con discinesia scapolare. La discinesia scapolare può determinare un aumento della forza di adduzione della spalla nei nuotatori.

Parole chiave. Discinesia, forza isometrica, atleti overhead, range di movimento.

Introduction

The shoulder joint is one of the most critical joints involved in overhead sports such as volleyball, tennis, handball, badminton, and especially swimming. Athletes participating in these disciplines are at a high risk of shoulder injuries due to repetitive overhead movements, often exceeding 90 degrees, as well as the significant force and load exerted on the shoulder1. The position and natural alignment of the scapula on the thoracic cage, both in static and dynamic states, play a crucial role in performing arm movements and preventing shoulder injuries2.

Proper strength and balance of the scapular muscles are especially important because the humerus and scapula move in harmony during arm movements, a motion referred to as the scapulohumeral rhythm3. Scientific evidence indicates that athletes who frequently engage in overhead movements, particularly swimmers, exhibit abnormal activity in the shoulder girdle muscles4 and altered shoulder kinematics and scapulohumeral rhythm4. The scapula should be positioned between the spinous processes of the second and seventh thoracic vertebrae, with approximately 30 degrees of protraction in the frontal plane5.

Scapular dyskinesis refers to abnormal changes in the position and kinematics of the scapula2,6. Such disorders affect the scapulohumeral rhythm and humerus movement6. Swimming may alter the position of the scapula, but it is unclear whether these changes are associated with shoulder pain7. Additionally, altered scapular motion may be linked to neck pain. Despite these findings, clinical evidence on whether shoulder pain leads to the development of scapular dyskinesis or vice versa remains limited8.

There is no direct and definitive correlation between shoulder injuries and scapular dyskinesis9. However, scapular dyskinesis is observed in 67% to 100% of athletes with shoulder injuries and in 61% of overhead athletes10. Scapular dyskinesis increases the risk of future shoulder pain by up to 43%11. The prevalence of scapular dyskinesis in swimmers has been reported to range from 8.5% to 63.6%12.

The exact etiology of scapular dyskinesis has not yet been fully established. There are multiple potential contributing factors, including bony pathology, joint pathologies, soft tissue inflexibility, and decreased muscle performance13. Among these, muscular imbalance plays a significant role. An imbalance between the trapezius, serratus anterior, levator scapulae, and pectoralis minor muscles can lead to dyskinesis14.

Alterations in shoulder girdle muscle strength, range of motion, and scapulohumeral rhythm have been identified as contributing factors to scapular dyskinesis15. Claessen et al. conducted a study investigating the relationship between scapular dyskinesis and shoulder range of motion. The results demonstrated a significant relationship between the presence of scapular dyskinesis, reduced overall shoulder range of motion, and decreased strength of external shoulder rotators in individuals with shoulder injuries16. Ozturk et al. demonstrated a statistically significant difference in shoulder flexion muscle strength between swimmers with and without scapular dyskinesis in both women and men. They also found significant differences in internal and external shoulder rotation muscle strength in men17. In contrast, Hannah et al. reported no difference in shoulder muscle strength between non-athletes with and without scapular dyskinesis13. Hajihosseini et al. found a significant difference in the scapulohumeral rhythm ratio between rest and 90 degrees, as well as at 135 degrees, in the dominant shoulders of female volleyball players with and without dyskinesis. However, no significant difference was observed at angles from rest to 45 degrees18.

Despite the importance of scapular dyskinesis in swimmers, there are limited quantitative studies comparing strength measurements between groups with and without scapular dyskinesis13. Given that abnormal scapulohumeral rhythm and scapular dyskinesis can affect a swimmer’s performance, the aim of the present study is to investigate the scapulohumeral rhythm, dyskinesis, as well as strength and range of motion in elite swimmers with and without scapular dyskinesis.

Materials and methods

This study employed a causal-comparative design and, based on its nature and objectives, is classified as applied research. Relevant measurements were collected, along with additional information from athletes through questionnaires and interviews conducted by the researcher. The study was conducted in accordance with the Declaration of Helsinki and approved by the Research Ethics Committees of University of Guilan approved on October 26, 2022. The patients and/or their families were informed that data from the research would be submitted for publication, and gave their consent.

Participants

The study population comprised elite swimmers, and relevant measurements were taken by the researcher during the national team selection competitions (short course swimming, 6th period, held in Mashhad from November 19 to November 20, 2022). Using G*Power sample size determination software, with an effect size of 0.84, a test power of 0.8, and a significance level of 0.05, the estimated sample size was 38 participants. To ensure robustness, one additional participant was included in each group.

A total of 40 elite swimmers, were purposefully selected and divided into two groups of 20 individuals with and without scapular dyskinesis based on inclusion criteria. Inclusion criteria included: male elite swimmers aged 16 to 25 years; a minimum of 2 years of experience in national swimming competitions or swimming leagues; at least 3 years of regular swimming activity; a positive result on the scapular dyskinesis test with dumbbells (1 kilogram for individuals weighing under 68 kilograms, and 2 kilograms for those over 68 kilograms)19; presence of scapular dyskinesis as indicated by the lateral scapular slide test; a normal body mass index (18.5–25 kg/m²); participation in at least 6 training sessions per week totaling 12 hours; no history of fractures, dislocations, complete tears, adhesive capsulitis, or muscle atrophy in the shoulder girdle; no history of injuries to the cervical and thoracic spine and clavicular; no history of shoulder girdle surgery or shoulder pain during exercise or normal conditions; no participation in any rehabilitation or therapeutic exercise programs in the past six months; no shoulder instability due to previous injury in the past 6 months; no restrictions in the range of motion of the shoulder joint; no severe abnormalities in the upper limb, including shoulder, neck, and spinal column (such as kyphosis). There were no apparent abnormalities in the lower limbs, pelvis, or spinal deviations, and no back disorders were observed in any of the swimmers. Following coordination and familiarization with the nature of the research, and after completing the informed consent form, the necessary information was collected.

Procedures

In the first stage, participants were evaluated based on the inclusion criteria. Scapular dyskinesis was assessed using the scapular dyskinesis test with dumbbells and the lateral scapular slide test (which identifies a difference of 1.5 centimeters or more between the two scapulae). Following this assessment, 40 individuals proceeded to the second stage of the research. Out of the 43 swimmers examined, 23 were identified with scapular dyskinesis. In the subsequent stages, anthropometric data, shoulder range of motion, isometric muscle strength of selected shoulder muscles, and scapulohumeral rhythm at three angles (45, 90, and 135 degrees) were measured and recorded in the appropriate forms (figure 1).

Scapular dyskinesis test

To determine the presence or absence of scapular dysfunction through visual observation, the subject stood with dumbbells and arms alongside their body, elbow straight, and shoulders in a neutral position. The examiner stood behind the subject. The subject was asked to raise both arms in the frontal and sagittal planes for three seconds and then lower them within three seconds. These movements were repeated five times, and the scapular movement pattern was observed during each repetition. Signs of scapular dysfunction included excessive elevation, protraction, prominence of the inferior angle, and prominence of the medial border at each movement level (table 1, figure 2)20,21.

Lateral scapular slide test

The lateral scapular slide test, developed by Kibler, involves marking the inferior angle of the scapula on the skin with a marker. The distance between this marked point and the adjacent vertebrae is measured along its own axis in three standing positions: arms by the sides, hands on the waist (thumbs posteriorly, four fingers anteriorly), and arms abducted at a 90-degree angle with thumbs facing downward. Each measurement was repeated three times for each arm, and the average of these measurements was calculated. A difference of 1.5 centimeters or more between the two sides in any of the measurements was considered a positive result for the test (table 1, figure 3)22.

Unlike previous studies, this research utilized both the lateral scapular slide test and the scapular dyskinesis test to evaluate the scapula in both static and dynamic states. If a participant was diagnosed with dyskinesis in either of the tests, they were placed in the group with dyskinesis.

Scapulohumeral rhythm

An inclinometer was used to measure shoulder abduction, and a second inclinometer was used to measure scapular upward rotation. The participant was asked to stand barefoot, fully extend their elbow, maintain a neutral wrist position, and slightly incline their thumbs towards the coronal plane. The first inclinometer was precisely positioned vertically just below the deltoid muscle and secured to the humerus with a strap. The participant was instructed to actively perform shoulder abduction and maintain the arm at 45, 90, and 135 degrees of abduction while keeping it extended. The degree of scapular upward rotation was measured using the second inclinometer placed on the scapular spine. The scapulohumeral rhythm was calculated by:

Participants performed each movement three times with their dominant arm, with a two-minute rest between each repetition. The average of these three movements was used for analysis23,24.

Assessing the range of motions

All range of motion measurements, including internal and external rotation, flexion, extension, abduction, and adduction, were conducted using a goniometer according to the method described by Berryman Reese and Bandy25. The dominant side was chosen for assessment.

Measurement of isometric strength

All muscle strength measurements were repeated three times, with the averages used for data analysis. A 30-second rest was provided between each measurement, and a 1-minute rest period was provided between each test17. A hand-held dynamometer (Manual Muscle Test - MMT) (manufactured by North Coast, USA) was used to measure the isometric strength of the shoulder girdle muscles.

The internal and external rotator muscles of the humerus

The maximum isometric strength test for external rotation (measuring the muscle power of the infraspinatus and teres minor): the participant lay flat in the prone position with the head turned to the side. The shoulder was at 90 degree abduction, the elbow fully supported on the bed, and the forearm hanging vertically from the edge of the bed. A rolled towel was placed under the humerus for support. A dynamometer was positioned near the radius styloid process on the posterior side of the wrist. The participant resisted the force applied toward internal rotation. The isometric force exerted by the participant was recorded on the digital dynamometer.

The maximum isometric strength test for internal rotation (measuring the muscle power of the subscapularis): the test was conducted similarly to the previous examination. The participant resisted the force applied outward for external rotation3,13.

Shoulder flexion, extension, abduction, adduction, protraction and elevation strength

Shoulder strength in flexion, extension, abduction, and adduction was measured according to the method described by Kendall et al.5.

Scaption strength

The participant was tested in a seated position with the shoulder abducted at a 75-degree angle, thumb was pointed upward, and forearm in a neutral position. One hand held the participant’s scapular stationary while the other hand held the dynamometer at the midpoint between the shoulder and elbow (between the acromion process and the lateral epicondyle of the humerus). In this position, the participant resisted against a force applied to lower the hand3,5.

Data analysis

All statistical analysis was conducted using IBM SPSS 25. Descriptive statistics were utilized for data classification and organization, determining central tendency and variability indices (mean and standard deviation), and for creating tables and graphs. The Shapiro-Wilk test was used to assess the normality of the data distribution. In the inferential statistics section, independent t-tests were employed to compare means between groups.

A p-value < 0.05 was considered statistically significant.

The data associated with the paper are not publicly available but are available from the corresponding author on reasonable request.

Results

Table 2 presents the demographic information of the participants, table 3 descriptive information (mean ± standard deviation) for variables including scapulohumeral rhythm, range of motion, isometric strength, and the results of data analysis. Except for shoulder extension range of motion (p=0.004) and shoulder adduction strength (p=0.048), no statistically significant differences were observed between the two groups with and without dyskinesis.

Discussion

In the study by Pashaei et al., which investigated the prevalence of movement impairments in the shoulder girdle and their effect on the stability of upper extremity function among elite volleyball players, findings indicated a significant relationship between these impairments and upper limb stability, which is consistent with the results of the present study19. Similarly, the study by Hajihosseini et al., which examined the scapulohumeral rhythm ratio in female volleyball players with and without scapular dyskinesis, found consistent results at the 45-degree angle. However, their findings at the 90 and 135-degree angles were inconsistent with the present study18. Considering that the study by Hajihosseini et al. was conducted on female volleyball players, while the present study involved male swimmers, it is essential to take sex differences into account when evaluating muscular injuries. These sex-related differences may play a significant role in the observed discrepancies in scapulohumeral rhythm across the examined angles26. Given that the study by Hajihosseini et al. was conducted on female volleyball players, the average height and weight in both the dyskinesis and without dyskinesis groups in the present study were higher.

According to the obtained results, the scapulohumeral rhythm ratio decreases with an increase in abduction angle in both groups. This finding is consistent with a study by Sree et al., which examined the scapulohumeral rhythm in 120 individuals with dyskinesis27. Additionally, a study by Hosseinimehr and Ambarian, which compared the scapulohumeral rhythm ratio among volleyball, handball, table tennis players and swimmers, found results consistent with the volleyball, handball, and table tennis players, but not with the swimmers28.

Studies have shown that during the initial 30 degrees of abduction or 45 degrees of flexion, the scapula either moves closer to or farther from the vertebral column to achieve stability on the chest. In the initial stages of abduction or flexion, most of the movement occurs at the glenohumeral joint. After 30 degrees of abduction or 45 to 60 degrees of flexion, the ratio of movement between the glenohumeral joint and the scapulothoracic joint shifts to 5:4, and it becomes 2:1 over the full range of motion29. Various studies have reported different ratios for scapulohumeral rhythm in the range of 1:1.7, 1:2.1, 1:2.4, 1:2.6. This variability in reported ratios is likely due to differences in measurement techniques and methodologies for defining and describing scapulohumeral rhythm. Given that an imbalance between scapular upward rotation and shoulder abduction may increase the risk of shoulder disorders, it is crucial for therapists to carefully assess scapular upward rotation and scapulohumeral rhythm18. Research indicates that scapulothoracic dysfunction plays a significant role in the development of glenohumeral pathology30. Scapulothoracic dysfunction is characterized by abnormal resting and movement positions of the scapula in relation to various shoulder pathologies31. These pathologies can include disruptions in scapulohumeral rhythm and reduced subacromial space during abduction32. Proper scapulothoracic rhythm relies on the appropriate activation of the scapular upward rotator muscles4.

In the study by Ozturk et al., which investigated isometric shoulder strength in swimmers with and without scapular dyskinesis, the results revealed a statistically significant difference in isometric strength for shoulder flexion, internal rotation, and external rotation among male swimmers with and without scapular dyskinesis. This finding is inconsistent with the results of the present study. However, for isometric strength in shoulder extension, no significant difference was observed between the two groups, which aligns with the present study’s results. Additionally, the study found a statistically significant difference in shoulder flexion strength between the two groups of female swimmers, which is not consistent with the findings of the present study17. One potential reason for the difference between the present study and the aforementioned research could be the variation in sample size. In the study by Öztürk et al., there were 26 male and 13 female participants in the scapular dyskinesis group and 8 male and 9 female participants in the group without dyskinesis. Another factor to consider is the difference in the average age of swimmers17. In the study by Öztürk et al. the average age of the swimmers was approximately 10 years17. Additionally, the findings are consistent with a study by Hannah et al., who concluded there is no statistically significant difference in shoulder muscle strength between non-athletic individuals with and without scapular dyskinesis13. Furthermore, a study by Nodehi et al. found that a statistically significant difference in the average isometric strength of scaption (with external rotation), abduction and scapula upward rotation, adduction and scapula downward rotation between individuals with and without scapular dyskinesis, which is inconsistent with the present study3. One possible reason for this discrepancy could be that the study by Nodehi et al. included female participants, some of whom might have had a sports history or athletes experience, which was not specified in the inclusion criteria. While, there is no statistically significant difference in the strength of internal and external rotation, which is consistent with the present study3. In the other words, compared to the control group, individuals with scapular dyskinesis demonstrated weaker strength in the supraspinatus, serratus anterior, middle and lower trapezius, and rhomboid muscles3. McLaine et al. reported that reduced shoulder extension strength is associated with shoulder pain in swimmers33. However, the authors noted that further research is needed to establish a causal relationship. This association may be attributed to an imbalance in the biomechanics of the shoulder rotator cuff muscles and a reduced ability to stabilize the scapula due to scapular dyskinesis33. Some studies suggest that physical therapy can be an effective approach for managing scapular dyskinesis and correcting abnormal biomechanics. Therefore, physical therapy for the shoulder muscles is essential in the rehabilitation of patients with shoulder impingement syndrome and scapular dyskinesis, as these muscles are vital for both the resting position and motion of the scapula. Considering the relationship between reduced strength in shoulder girdle motions with dyskinesis, strengthening the shoulder girdle muscles, especially the supraspinatus, serratus anterior, rhomboids, and middle and lower trapezius muscles, appears to be crucial3,34.

One of the reasons for the differences in the results between the present study and previous research may be the use of both the scapular dyskinesis test and lateral scapular slide test for diagnosing scapular dyskinesis in the participants. Another factor to consider is the bilateral nature of arm motion in swimmers compared to unilateral sport disciplines practitioners.

It is recommended to measure scapular upward rotation and scapulohumeral rhythm at 45, 90, and 135 degrees of humeral flexion, the scapulohumeral rhythm should also be evaluated at different angles and during movement, various swimming styles (breaststroke, backstroke, butterfly, freestyle) should be examined to assess dyskinesis and scapulohumeral rhythm, additionally, measuring strength, range of motion, and scapulohumeral rhythm in the non-dominant shoulder and comparing both sides is advised.

Conclusions

There is no significant difference in scapulohumeral rhythm at 45, 90, and 135 degrees between the two groups. It is suggested that with increasing age and sports history, the differences in scapulohumeral rhythm between groups with and without dyskinesis may become more pronounced. Given the lower average range of motion observed in the dyskinesis group, it is advisable to consider exercises to increase the range of motion for these swimmers. Scapular dyskinesis may lead to an increase in shoulder adduction strength in swimmers. Statistically, there is no difference in shoulder flexion, extension, abduction, external rotation, internal rotation, shoulder protraction, scaption and scapular elevation strength between the two groups. However, the average strength in the dyskinesis group was lower compared to the without dyskinesis group. Overall, further research is needed to draw definitive conclusions about the differences in scapulohumeral rhythm, strength, and range of motion between swimmers with and without dyskinesis.

Conflicts of interest. The authors declare that there is no conflict of interest.

Authors’ contribution. FS: writing - review and editing, formal analysis, data curation, methodology, roles/writing - original draft, software. AAN: writing - review and editing, supervision, project administration. LY: writing - review and editing, supervision, methodology.

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