Relation Between Swimming Stroke Types And Scapular Dyskinesia In Swimmers: A Cross - Sectional Study

Swimming, as an overhead sport, exert significant mechanical stresses to the shoulder complex and high rate of overuse injuries, especially around the glenohumeral and scapulothoracic joints . For competitive swimmers, the high training volume and nature of repeated elevation of the arms imposed by different strokes leading to abnormal scapular motion commonly termed scapular dyskinesia (SD).

The repeated overhead motion of swimming strokes can produce microtrauma to the passive stabilizers of the glenohumeral joint and fatigue of the dynamic stabilizers, especially the rotator cuff and scapular stabilizers . Over time, this repetitive loading may contribute to muscle imbalance between agonist and antagonist groups, such as internal versus external rotators, and between the upward rotators (serratus anterior, lower trapezius) and downward rotators (levator scapulae, rhomboids).

These imbalances can lead to decreased range of motion (ROM), altered scapular positioning, and the development of scapular dyskinesia, which may be present even in overhead athletes who are initially asymptomatic. It's stated that shoulder impingement accounts for approximately 44% to 65% of all shoulder complaints in clinical examinations.

The adaptive shortening or tightness of the pectoralis minor muscle (PMm) is one of the potential biomechanical mechanisms associated with altered scapular alignment at rest and scapular motion during arm elevation

(scapular dyskinesis) in patients with shoulder complaints . SD is common in elite swimmers and is associated with shortened pectoralis minor, reduced IR ROM, and impaired shoulder function, although it may not be directly related to pain. In swimmers, repetitive overhead stroke cycles and sport-specific training demands may contribute to adaptive changes in anterior shoulder structures and altered scapular kinematics during arm elevation.

A lot of research has documented that a high prevalence of scapular dyskinesia among competitive swimmers even asymptomatic healthy athletes, and has linked dyskinesia to altered scapular kinematics and increased risk of shoulder complaints.

The prevalence of scapular dyskinesia among swimmers varies widely across studies; for example, a recent cross-sectional study reported that 71.1% of male swimmers and 50% of female swimmers demonstrated scapular dyskinesia on clinical testing.

Epidemiological data indicate that the prevalence of subacromial impingement in large swimmer samples can be around 37%, with similar rates in male and female swimmers , and recently it's stated that the prevalence of subacromial impingement among Egyptian swimmers were 37.3%.

Competitive swimming comprises four main strokes-freestyle, butterfly, backstroke, and breaststroke-each with distinct kinematic patterns and loading profiles for the shoulder girdle.

Because of stroke-specific kinematic patterns and loading profiles, swimming strokes have been hypothesized to produce distinct shoulder adaptations and injury risks, and several studies have examined whether stroke specialization influences shoulder pain and shoulder function in competitive swimmers.

Freestyle and backstroke are classified as long-axis strokes because they involve axial body rotation with alternating arm movements and repetitive overhead shoulder motion, resulting in high cyclic loading on the glenohumeral and scapulothoracic joints. Freestyle is performed in a prone position, whereas backstroke is performed in supine. In contrast, butterfly and breaststroke are considered short-axis strokes due to their more symmetrical movement patterns and greater trunk flexion-extension or undulatory motion. Butterfly requires simultaneous powerful overhead arm actions combined with a dolphin kick, producing substantial mechanical stress on the shoulder girdle. Breaststroke involves a more horizontal sweeping arm motion with less overhead elevation and generally lower shoulder stress, although repetitive abduction and external rotation may still load the shoulder structures.

Although stroke-specific mechanical demands have been suggested to influence shoulder loading patterns, the relationship between different stroke specializations and scapular mechanics has not been sufficiently explored. Furthermore, existing research has primarily emphasized the prevalence of scapular dyskinesis and its association with injury or pain, with less attention given to underlying biomechanical factors such as muscle strength, flexibility, and joint range of motion.

In addition, few studies have comprehensively examined multiple intrinsic factors as (scapular muscle strength, pectoralis minor flexibility, posterior shoulder tightness, and glenohumeral internal rotation) in relation to stroke specialization. Lack of integrated biomechanical assessment limits the understanding of how sport-specific movement patterns may influence scapular function. Therefore, there is a need for further investigation into the association between different swimming stroke types and key biomechanical variables, including scapular dyskinesis, muscle strength, flexibility, and range of motion in competitive swimmers.

Statement of the problem:

The current study will be conducted to answer the following questions:

• Is there a relation between swimming stroke type (Freestyle, Breaststroke, Backstroke and Butterflystroke) and A. Scapular dyskinesia? B. Scapular muscles' strength (Serratus anterior, middle trapezius and lower trapezius)? C. Pectoralis minor flexibility? D. Posterior shoulder capsular tightness? E. Glenohumeral internal rotation ROM?

Purpose of the study:

• To investigate the relation between swimming stroke type (Free style, Breast stroke, Back stroke and Butterfly stroke) and A. Scapular dyskinesia.

1. Scapular muscles' strength (Serratus anterior, middle trapezius and lower trapezius).
2. Pectoralis minor flexibility. D. Posterior shoulder capsular tightness. E. Glenohumeral internal rotation ROM.

Significance of the study:

Adolescent swimmers are at considerable risk of overuse injuries, with the shoulder being the most frequently affected region 91% of young elite swimmers aged 13-25 years experienced at least one episode of shoulder pain, while 84% demonstrated a positive clinical impingement sign, indicating a high burden of shoulder pathology in this age group.

The high prevalence of shoulder injuries in swimmers has been closely linked to alterations in scapular mechanics, particularly scapular dyskinesis (SD), which is commonly observed in overhead athletes.

In swimmers, SD has been reported in both symptomatic and asymptomatic individuals, indicating that it may develop as a result of repetitive loading and sport-specific adaptations rather than pain alone.

So, investigating the relationship between swimming stroke types and scapular dyskinesis is essential to better understand the biomechanical factors contributing to shoulder injuries in swimmers. Such understanding may help in developing effective injury prevention strategies, improving rehabilitation approaches, and enhancing overall athletic performance.

Assumptions:

It will be assumed that:

1. All swimmers will be representative of adolescent Competitive Swimmers with specific Stroke Type.
2. All participants will perform the required assessment procedures to the best of their ability.
3. All participants will follow the given instructions during testing procedures

Hypotheses:

1. There will be no significant relation between different swimming stroke types and scapular upward rotation angle
2. There will be no significant relation between swimming stroke type and scapular muscle strength A. Serratus anterior muscle B. Middle trapezius muscle C. Lower trapezius muscle
3. There will be no significant relation between swimming stroke type and pectoralis minor length
4. There will be no significant relation between swimming stroke type and posterior shoulder tightness
5. There will be no significant relation between swimming stroke type and glenohumeral internal rotation

Biomechanics of Swimming and Stroke Types Competitive swimming comprises four main strokes-freestyle, backstroke, butterfly, and breaststroke-each characterized by specific body positions, movement patterns, and propulsion strategies. Long-axis strokes (Freestyle, backstroke) involve rotation around the swimmer's longitudinal axis, whereas short-axis strokes (butterfly, breaststroke) emphasize trunk flexion-extension and undulatory motion.

Freestyle propulsion is primarily generated through an alternating arm cycle that includes hand entry, catch, pull-through, push, and recovery, coordinated with a flutter kick to maintain streamlined body position.

During the underwater phases, the shoulder moves through substantial flexion, internal rotation, and horizontal adduction, while the rotator cuff and scapular stabilizers Efficient technique requires coordinated trunk rotation, stable scapular control-especially by the serratus anterior-and a continuous flutter kick to maintain body alignment and reduce drag act, scapular motion under hydrodynamic load can increase anterior shoulder stress and impingement risk.

Backstroke uses a similar alternating arm pattern but is performed in a supine position, with each arm recovering overhead and then executing an underwater pull as the trunk rotates around the long axis. Although the shoulder is oriented differently than in freestyle, backstroke still involves repetitive overhead elevation and rotation, subjecting the glenohumeral and scapulothoracic joints to high volumes of cyclic loading.

The powerful phase of pull-through relies heavily on the teres minor and subscapularis, which must act as both power and endurance muscles, making them susceptible to fatigue and contributing to impaired humeral head depression and potential impingement.

In butterfly, the hands enter the water together in front of the shoulders while the upper body "presses" down, then follow an S-shaped pulling pattern under the body before extending and exiting the water to begin a simultaneous arm recovery. However, excessive humeral hyperextension during pull-through and increased internal

rotation stress at arm exit may elevate shoulder loading. Additionally, inadequate activation or fatigue of stabilizing muscles such as the serratus anterior and teres minor can impair scapular control and humeral rotation, predisposing swimmers to shoulder impingement and pain.

This stroke is considered particularly demanding because it requires large, simultaneous excursions of shoulder flexion and internal rotation with high propulsive forces, leading to substantial mechanical stress on the shoulder girdle.

Breaststroke differs from the other swimming strokes because the arms remain primarily in front of the body and move in a horizontal semicircular pattern with minimal axial rotation and less extreme overhead elevation. The stroke consists of an outsweep, insweep, and recovery phase, beginning from an extended streamline position and ending with the hands meeting in front of the chest before forward recovery.

Propulsion is generated through the coordinated action of the arm movements and the symmetric whip kick, which distributes the mechanical load more evenly between the upper and lower limbs. Consequently, breaststroke generally places lower mechanical stress on the shoulders compared to other strokes. However, excessive shoulder abduction, external rotation during the outsweep, and increased internal rotation during pull-through may still contribute to shoulder overuse injuries when technique or training load is inadequate.

These stroke-specific biomechanical differences may lead to distinct shoulder loading patterns and muscle demands, and these variations have been implicated in the development of scapular dyskinesis and other shoulder-related problems in swimmers.