**4. Discussion**

This study is the first one that had explored the association of the forward shoulder angle and the pectoralis minor index in volleyball players. To summarize, the two main principal findings of this study are as follows:


#### *4.1. Posture*

The results of this study appeals to the fact that shoulder position is not a key factor or a clear contributor to shoulder pain [11,22]. These results are in agreement with the findings of Ozunlu et al. [23] and Ribeiro et al. [23] Ozunlu et al. [23] showed that asymmetric scapular posture in volleyball players might be normal and not necessarily related to injury and Ribeiro A et al. [23] reported that scapular asymmetry may be normal and it should not be automatically considered as a pathological sign in throwing athletes. This situation has also been related to other areas of the body, such as the low back region, where there is no correlation between imaging tests and pain [24].

Precisely and related to PMI, several recently conducted studies concluded that there is no association between shoulder pain and function with the length of the pectoralis minor in patients with chronic shoulder pain [25,26]. This is consistent with our results although they are not performed in a sports population.

Although it has been found in another study that patients with forward shoulders have greater scapular internal rotation and less serratus anterior activity, these alterations are not associated with shoulder pain [6]. Therefore, although it has been proposed that the round shoulder posture may be related to shoulder pain and dysfunction because it alters the kinematics and muscle activity generating stressful situations in the shoulder, it seems that this relationship cannot always be established [27]. Perhaps clinical reasoning should be based more on dynamic observation of posture rather than static observation of posture [28].

It has been suggested that in the assessment of shoulder posture in patients with shoulder pain it could be interesting to observe how the change in shoulder posture affects the signs and symptoms of the patient with shoulder pain [29]. Lewis JS et al. showed that changing posture in patients with shoulder pain had positive effects on mobility and pain in these subjects [29]. A cohort study investigated people with shoulder pain and concluded that the best prognostic factor for these patients was the change of symptoms during the modification of scapula posture in the arm elevation movement [30]. Therefore, postural alteration would be clinically relevant when postural modification during the assessment of the patient with shoulder pain also modifies the patient's signs and symptoms [28]. On the other hand, demonstrating to a patient that symptoms are modifiable could give the individual confidence to move and better adherence to treatment [31].

#### *4.2. Mechanical Hyperalgesia*

The relationship between posture and tissue mechanosensitivity has been studied previously. Although the mechanical stress suffered by the structures involved in a poor posture could produce an alteration of the sensitivity of these structures, it seems that the presence of pain plays an important role in the degree of mechanosensitization [7,32,33]. Martinez-Merinero P et al. [7], Rojas VEA et al. [32], and Pacheco J et al. [33], showed that mechanosensitivity of neck muscles and upper extremity nerve trunks is related to neck pain more than to forward head position. Similarly, a study conducted by Haik M et al. [34] in which they found that subjects with shoulder pain demonstrated mechanical hyperalgesia compared with healthy controls.

The results obtained in our study have shown that the mechanosensitivity of the assessed muscles is related to shoulder pain and not with rounded shoulder posture. The infraspinatus, levator scapulae, and pectoralis major muscles were shown to have greater mechanical hyperalgesia in volleyball players with shoulder pain. These data are consistent with the results of Hidalgo-Lozano et al. reporting that elite swimmers with shoulder pain showed significant lower PPT in levator scapulae, sternocleidomastoid, upper trapezius, and infraspinatus compared with healthy athletes [35]. Pain and altered mechanosensitivity could be a consequence of repetitive overhead movements. The infraspinatus, levator scapulae, and pectoralis major muscles can produce shoulder pain [36]. In particular, the infraspinatus muscle has been shown to be important in shoulder problems [37,38]. It is a structure involved in functional problems and shoulder pain [37,38]. During a sports competition, volleyball players with shoulder pain were treated for the infraspinatus muscle and the players were able to continue in the competition [37].

On the other hand, another interesting finding of this study was the relationship the pectoralis minor index with mechanical hyperalgesia of the ulnar nerve. The pectoralis minor index expresses the length of the pectoralis minor muscle [16]. The association between a decrease in pectoralis minor length and shoulder pain has been described in athletes [39]. And pectoral shortening as a factor associated with volleyball-related shoulder pain and dysfuntion [40]. During arm elevation, subjects with shortened pectoralis minor showed decreased external rotation/retraction and posterior tilting of the scapula [40]. Limitation of scapular movements could compromise the pectoralis minor space and increase mechanical stress on the ulnar nerve [40]. Increased mechanical stress on the ulnar nerve could lead to pain and other neurogenic alterations in the upper extremity [41].

Although the relationship between the pectoralis minor muscle and the ulnar nerve has not been studied to our knowledge, it could be a cause of shoulder pain in all overhead activities.

#### *4.3. Clinical Implications*

Establishing a definitive structural diagnosis for an athlete presenting with shoulder pain is a difficult process. There appears to be a poor correlation between orthopedic and imaging tests and symptoms related to shoulder pain. In this regard, postural deviations have been frequently cited as a cause of shoulder pain and disability. This study, like others, challenges this approach. Therefore, the importance of postural disturbances during the assessment of a subject with shoulder pain should be approached differently. The shoulder forward posture may not be related to shoulder pain.

On the other hand, it seems that the shoulder musculature could be one of the causes of pain in these patients. During spiking in volleyball there is a significant increase in activity and stress on the shoulder musculature [42]. Probably, repeated overhead movements may produce an increase in mechanical muscle hyperalgesia. The mechanical muscle hyperalgesia could translate into increased tension and onset of shoulder pain.

Treatment of the infraspinatus, levator scapulae, pectoralis major, and pectoralis minor muscles could improve shoulder pain and ulnar nerve mechanosensitivity.

The literature suggests that mechanical hyperalgesia is related to poorer muscle function, and this leads to poorer motor control recruitment [35,43–45]. In sport medicine, this can be key factor in both prevention and injury recovery. Therefore, the results of this study suggest that the shoulder forward posture or the pectoralis minor index does not appear to be associated with shoulder pain, but yes, the mechanical hyperalgesia of the shoulder complex musculature. Therefore, an assessment of mechanical hyperalgesia in athlete patients with shoulder pain is suggested before posture. We can therefore suggest that in the examination of these patients it would be advisable to pay attention to the signs and symptoms of pain processing rather than to assessing shoulder posture.

#### *4.4. Limitations*

One of the main limitations of this study is that it is a cross-sectional study can only demonstrate association and not causation. Longitudinal studies are now needed to determine the role of mechanical hyperalgesia and posture in the development of shoulder pain in volleyball players. In addition, one of the limitations due to the small sample size and high effect size established, is that smaller correlations may exist. The population size was small. Future studies with larger samples are needed to further confirm the current results.

#### **5. Conclusions**

No association was found between the forward shoulder angle and the pectoralis minor index in volleyball players with and without shoulder pain. There is a moderate negative association between shoulder forward angle and muscle mechanical hyperalgesia in volleyball players with shoulder pain, but no such associations were found in volleyball players without shoulder pain. Treatment of the infraspinatus, levator scapulae, pectoralis major, and pectoralis minor muscles could improve shoulder pain and ulnar nerve mechanosensitivity.

**Author Contributions:** Conceptualization, D.P.-M., S.P.-N., J.Q.-P. and T.G.-I.; methodology D.P.-M., H.B.-A. and J.F.-C.; validation, all authors; formal analysis, H.B.-A. and J.F.-C.; investigation, all authors; resources, D.P.-M. and T.G.-I.; data acquisition, G.C.-R. and C.Q.-S.; writing—original draft preparation, D.P.-M., H.B.-A. and J.F.-C.; writing—review and editing, all authors; supervision, all authors; project administration, D.P.-M.; funding acquisition, D.P.-M. All authors have read and agreed to the published version of the manuscript.

**Funding:** Part of Hector Beltran-Alacreu's salary is financed by the European Regional Development Fund (2020/5154).

**Institutional Review Board Statement:** The Research Ethics Committee of University CEU Cardenal Herrera from Valencia (CEI16/0112).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study. Written informed consent has been obtained from the patient(s) to publish this paper.

**Data Availability Statement:** Data available on request due to privacy and ethical restrictions.

**Conflicts of Interest:** The authors certify that they have no affiliations with or financial involvement in any organization or entity with a direct financial interest in the subject matter or materials discussed in the article.

#### **References**

