Scapular asymmetry in tennis players: differential diagnosis and biomechanical insights| Lo Scalpello - Journal

Abstract

Objectives. To analyze the clinical significance of scapular asymmetry in tennis players and its differential diagnosis with scoliosis.

Methods. Narrative review of biomechanical and clinical literature on overhead athletes, focusing on rotator cuff adaptations and inertial loading mechanisms.

Results. Evidence indicates that scapular asymmetry in tennis players is associated with predominance of internal rotators, reduced external-to-internal rotator strength ratio, and repeated exposure to high inertial forces during overhead movements.

Conclusions. Scapular asymmetry is more likely to represent a functional neuromuscular adaptation rather than a structural spinal deformity. Correct interpretation is essential to avoid misdiagnosis and to guide appropriate orthopedic evaluation.

Introduction

Overhead sports are characterized by repetitive high-velocity movements of the upper limb, leading to specific adaptations of the musculoskeletal system, particularly involving the shoulder girdle and thoracic spine ^1-4. Tennis represents one of the most extensively studied models of these adaptations due to the combination of speed, asymmetrical loading, and complex kinetic chain involvement.

In clinical practice, shoulder height asymmetry is frequently observed in tennis players, often presenting as an apparent lowering of the dominant shoulder. This finding has sometimes been interpreted as a possible indicator of scoliosis. However, scoliosis is a three-dimensional structural deformity of the spine, defined by lateral deviation associated with vertebral rotation and confirmed radiographically, and isolated shoulder asymmetry does not constitute a diagnostic criterion ^5-7.

1. Recent biomechanical and clinical evidence suggests that scapular asymmetry in overhead athletes more often reflects functional adaptations of the scapulohumeral complex ^4,8-10, rather than a structural spinal pathology.

Muscle adaptations in overhead athletes

Athletes involved in overhead sports exhibit specific adaptations of the rotator cuff and scapular stabilisers ^11-13. In tennis players, isokinetic studies consistently demonstrate greater strength of the internal rotators in the dominant shoulder compared with the external rotators ^14-16.

The external-to-internal rotator strength ratio (ER/IR ratio) ^17-19 represents a key parameter in shoulder assessment.

The proposed biomechanical hypothesis

The central interpretative element of the present review is the biomechanical hypothesis that scapular asymmetry in tennis players may arise from the combined effect of two sport-specific factors: the functional predominance of the internal rotators of the dominant shoulder and the repeated exposure to high inertial forces generated during the serve and forehand.

This hypothesis does not imply a direct or exclusive causal relationship, but rather offers a clinically coherent model through which a common postural finding in tennis players may be interpreted in light of current biomechanical knowledge. Within this framework, the apparent lowering of the dominant shoulder is considered a potential expression of chronic adaptation of the scapulohumeral complex rather than a sign of structural spinal deformity.

From an anatomical and functional perspective, the glenohumeral joint is characterized by a natural predominance of internal rotators, including the pectoralis major, latissimus dorsi, teres major, and subscapularis. These muscles are not only more substantial in terms of muscle mass, but also capable of producing greater torque than the external rotators, represented mainly by the infraspinatus and teres minor.

In tennis, this physiological imbalance is amplified by the technical demands of the sport. During the acceleration phase of the serve and forehand, the dominant shoulder performs powerful internal rotation at extremely high angular velocities, exceeding 2000°/s in high-level players ^4,20,21. Repeated activation of the internal rotators under these conditions may promote selective strengthening, relative hypertrophy, and progressive reduction of the external-to-internal rotator strength ratio.

At the same time, the external rotators are required mainly to provide eccentric control during deceleration, rather than contributing directly to propulsion. This functional difference may progressively orient the neuromuscular system towards internal rotation dominance, with possible consequences for scapular resting posture and dynamic control.

According to the proposed hypothesis, this long-term predominance of internal rotator function may favor a chronic asymmetrical loading pattern of the shoulder girdle, which, together with inertial stresses acting on the dominant upper limb, may contribute to clinically observable scapular asymmetry.

This interpretation is consistent with the literature on overhead athletes ^12-22,24,25, in which scapular dyskinesis, altered rotator cuff balance, and kinetic chain adaptations have all been described as potential contributors to asymmetrical shoulder posture. The originality of the present model lies in bringing these elements together within a unified biomechanical explanation centered on the specific role of internal rotator predominance.

Role of inertial forces of the dominant limb

An additional key element of the proposed biomechanical hypothesis is the role of inertial forces generated by rapid movement of the dominant upper limb. According to the principles of dynamics ²³, these forces are proportional to segment mass and angular acceleration.

In tennis, the serve and forehand expose the shoulder girdle to substantial inertial stresses. These loads must be absorbed and controlled by the rotator cuff, scapular stabilizers, and surrounding musculature. Repeated exposure to such forces over time may contribute to chronic adaptation of the shoulder girdle, including altered scapular resting position and side-to-side asymmetry.

Within the proposed model, inertial loading does not act in isolation, but interacts with the pre-existing functional predominance of the internal rotators. The repeated combination of propulsive internal rotation and inertial demand may therefore produce a cumulative adaptive effect on the dominant shoulder.

This combined mechanism provides a plausible explanation for the frequent observation of a relatively lower dominant shoulder in tennis players, without necessarily implying vertebral deformity or scoliosis. In this respect, the model should be regarded as an interpretative biomechanical framework with direct clinical relevance, particularly in the orthopedic assessment of overhead athletes.

Differential diagnosis with scoliosis

Scoliosis is defined as a structural, three-dimensional deformity of the spine characterized by lateral curvature and vertebral rotation, confirmed by radiographic assessment using the Cobb angle ^5-7.

In contrast, scapular asymmetry represents a non-specific clinical finding that may be observed in healthy individuals, particularly in athletes exposed to asymmetric loading conditions (Fig. 1).

Therefore, shoulder height asymmetry alone should not be considered indicative of scoliosis. A correct diagnostic approach requires comprehensive clinical evaluation, including spinal assessment and, when appropriate, imaging studies.

From an orthopedic standpoint, failure to recognize this distinction may lead to overdiagnosis and unnecessary diagnostic procedures.

Clinical implications

Recognition of the adaptive nature of scapular asymmetry in tennis players has several important clinical implications.

First, it reduces the risk of misdiagnosis of scoliosis based solely on shoulder asymmetry. Second, it highlights the importance of functional assessment of the shoulder girdle in overhead athletes. Third, it supports the implementation of preventive and rehabilitative strategies aimed at restoring muscular balance between internal and external rotators and improving scapular stability.

Such interventions are central to prevention of shoulder injury in overhead sports.

Discussion

The present review proposes a clinical and biomechanical reinterpretation of scapular asymmetry in tennis players through integration of current literature on overhead sports with the proposed model ⁴. Shoulder height asymmetry has long been discussed in both medical and sports literature. Historically, this finding has sometimes been interpreted as a possible indicator of scoliosis, particularly in athletes engaged in unilateral disciplines. However, structural scoliosis is a three-dimensional spinal deformity characterized by lateral deviation and vertebral rotation, persisting independently of posture, and cannot be diagnosed on the basis of shoulder asymmetry alone ^5-7.

Over recent decades, biomechanical studies have documented sport-specific adaptations affecting the dominant shoulder in overhead athletes. Several interpretative models of scapular asymmetry have emerged in the literature (Tab. I).

Further interpretations concern glenohumeral mobility changes^17,26, including reduced internal rotation and altered rotator cuff balance, both commonly described in overhead athletes. Within this framework, scapular asymmetry is likely the result of a complex interaction of neuromuscular and biomechanical adaptations rather than a single mechanism.

The proposed biomechanical model is positioned within this interpretative context and offers a unifying explanation based on the predominance of internal rotators and the role of inertial forces⁴. Anatomically, internal rotators – including pectoralis major, latissimus dorsi, teres major, and subscapularis – have greater muscle mass and torque-generating capacity than external rotators. This intrinsic advantage is further amplified by the functional demands of overhead sports.

During the tennis serve and forehand, powerful internal rotation occurs during the acceleration phase, with angular velocities exceeding 2000°/s in elite players^4,20,21. Repeated exposure to such conditions promotes selective strengthening of internal rotators and a reduction in the external-to-internal rotator strength ratio. External rotators, conversely, act mainly eccentrically during deceleration^4,21,26, reinforcing the functional predominance of internal rotation.

In addition, inertial forces generated by rapid upper limb movement contribute significantly to loading of the shoulder girdle²³. Chronic exposure to these forces may induce long-term adaptations^24,25 in scapular positioning and muscle balance.

Within this biomechanical perspective, the apparent lowering of the dominant shoulder in tennis players is more plausibly interpreted as a functional adaptation of the scapulohumeral complex rather than a manifestation of spinal deformity⁴. Importantly, the proposed model does not imply a direct causal relationship but represents a physiopathological interpretation consistent with current evidence.

From a clinical standpoint, careful interpretation of scapular asymmetry is required. Shoulder asymmetry alone is not indicative of scoliosis and should be assessed within the broader context of sport-specific adaptations. Proper differential diagnosis requires comprehensive spinal examination and, when indicated, radiographic confirmation.

Conclusions

Scapular asymmetry is a common finding in tennis players and should be interpreted within the framework of sport-specific biomechanical adaptations rather than as an isolated clinical sign. The model proposed in this review suggests that this finding may arise from the combined effect of internal rotator predominance and repetitive inertial loading during high-velocity movements.

From a clinical perspective, scapular asymmetry in overhead athletes is more plausibly indicative of a functional adaptation of the scapulohumeral complex than of a structural spinal deformity. Recognizing this distinction is essential to avoid misdiagnosis, reduce unnecessary imaging, and support more accurate and clinically relevant decision-making.

Funding

This study received no external funding.

Conflict of interest statement

The authors declare no conflict of interest.

Authors’ contributions

R.L. conceived the study and drafted the manuscript. M.P. contributed to sports-specific interpretation. S.C. contributed to clinical interpretation and critical revision. All authors approved the final version.

Ethical consideration

Ethical approval was not required as this study is a narrative review based exclusively on previously published literature and does not involve human participants or patient data.

History

Received: March 25, 2026

Accepted: May 15, 2026

Published online: June 12, 2026

Figures and tables

Figure 1.Scapular asymmetry in a right-handed tennis player.

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