Comparison of electromyographic activity of selected shoulder girdle muscles and scapulohumeral rhythm of handball, tennis and swimmers during arm elevation at scaption level

Dissertation submitted as part of the academic activities required to obtain a Ph.D degree in the field of physical education and sports science, sports biomechanics

Abstract:

The aim of the present study is to investigate and compare the electromyographic activity of selected shoulder girdle muscles and scapulohumeral rhythm of handball players, tennis players, swimmers and Non-athletes during arm elevation at the level of scapulation in the superior and non-superior shoulder were under load conditions (25% of the maximum isometric strength of the abductors) and without load. 30 male athletes working in the main leagues of the country (10 swimmers, 10 handball players, 10 tennis players) and 10 non-athletes voluntarily participated in this research. Electromyographic activity of shoulder muscles (middle and anterior deltoid, upper, middle and lower trapezius, infraspinatus, latissimus dorsi, and anterior teeth) in parameters of call pattern, activity level and co-contraction ratio during arm abduction (at angles of 0-45 degrees for 1 second, 0-90 degrees for 2 seconds, 0-135 degrees for 3 seconds, 0-160 degrees for 4 seconds) and Its maintenance (at angles of 45, 90, 135 degrees for 3 seconds) at the level of scapulation using a surface electromyography device, as well as the scapulohumeral rhythm in different ranges of arm abduction at the level of scapulation, using measurements made with an inclinometer and the technique of taking photos in the superior and non-superior shoulder with and without external load were compared within and between these groups. The results of the study showed that the external load has a significant effect on the muscle recruitment pattern of the shoulder complex during arm abduction at the level of scapulation, but the pattern of muscle recruitment in the superior and non-superior shoulder during arm abduction at the level of scapulation was similar. Also, no significant difference in the pattern of muscle recruitment was observed between the different research groups during arm abduction at the level of scapulation (p<0.05). On the other hand, the results showed that the external load, the superior or non-superior hand and the abduction angle have an effect on the activity level and co-contraction ratio of the shoulder complex muscles during arm abduction (dynamic abduction) and its maintenance (static abduction) at the level of abduction, and there is a significant difference in the activity level and co-contraction ratio of the shoulder complex muscles during arm abduction and its maintenance at the abduction level between the research groups (p<0.05) also during arm abduction at the level Scapulation of the scapulohumeral rhythm in the superior shoulder was lower than in the non-superior shoulder, and handball players had a lower scapulohumeral rhythm compared to non-athletes (p<0.05). It is suggested that clinicians should be aware that some differences in the shoulder complex between overhead throwers and non-athletes may be normal and should not be considered as signs of shoulder pathology, but due to their shoulder adaptation to training and overuse of their upper limbs.

Key words: scapulohumeral rhythm, nature of sport, shoulder complex muscles, electromyography, overhead throwers. Head

-1 Introduction

Shoulder joint biomechanics is an interesting field of research that has attracted the attention of many researchers. The shoulder's ability to perform wide movements is based on the interaction of many structures that react to mechanical stimuli and adapt accordingly. The bone stability of the shoulder joint is not significant because there is a complete mismatch between the proximal articular surfaces of the arm and the glenoid fossa[1]. The addition of fibrous cartilaginous labrum, as well as the presence of joint capsule and ligaments of the glenohumeral joint increase the stability of the shoulder joint. In addition to static stabilizing structures, the stability of the shoulder joint is further supported by the muscles around the shoulder girdle, which provide dynamic stability of the shoulder. In fact, the dynamic and static stabilizers of the shoulder joint react against the forces applied to the shoulder joint in order to create stability in different positions, during different movements of the shoulder joint (Lugo et al, 2008).

The complex movements of the shoulder complex include coordinated movements in the acromial joints [2], sternoclavicular [3], glenohumeral [4] and scapulohumeral [5].The shape of the glenohumeral joint and the excitability of the scapula in relation to the chest is the main responsible for the excitability of this joint complex (shoulder complex) (Forte et al, 2009). The contribution of the scapulothoracic joint [6] to the kinematics of the normal shoulder complex was first described by Cathcart [7] (1884). Codman [8] (1934) defined the kinematic interaction between the shoulder and the arm as the scapulohumeral rhythm [9] (Codman, 1934). After Cadman, this definition is known as a valid method for analyzing the dynamic movements of the shoulder complex with a ratio of 2:1 (during full abduction of the arm, for every two degrees of movement in the glenohumeral joint, one degree of movement takes place in the scapulothoracic joint. In other words, in 180 degrees of shoulder abduction, there is 120 degrees of movement in the glenohumeral joint and 60 degrees in the scapulothoracic joint. (Inman et al, 1994). Such integration (coordination) allows the scapula to create a stable surface for glenohumeral movements and also allows optimal movement of the arm during full range of motion (Lugo et al, 2008). If the position of the shoulder changes, this normal pattern of integrated movements may be affected. For this reason, the scapulohumeral rhythm is considered as a movement index of the shoulder complex in clinical studies (Hebert et al, 2002, Myers et al, 2005, Ludewig et al. 2009).

Studies have shown that the normal scapulohumeral rhythm requires proper activity of the upper scapular rotators (De Mey et al, 2009, Luime et al., 2004). The upper rotators of the scapula are the upper trapezius, lower trapezius and anterior teeth (De Mey et al, 2009, Luime et al, 2004). In general, these muscles are important in achieving the full range of forward flexion and abduction of the shoulder (Ekstrom et al, 2003).

It is thought that during the elevation of the arm in the case of proper kinematics of the scapula, the volume of the subacromial space is maximized, thus reducing the prevalence of internal and external entrapment of the rotator cuff muscles. Lehman et al, 2007, Lukasiewicz et al, 1999)). Studies have shown that the greatest risk for impingement is when the scapula is inwardly rotated, anteriorly tilted, and has high reduced rotation. This risk increases when abduction is performed at the scapular level with internal rotation (Escamilla et al, 2009). Warner and his colleagues [10] (Warner et al, 1990) reported evidence for the association of shoulder impingement with wing-shaped scapula and scapular dysfunction. Researchers have also reported that the anterior teeth muscle, which produces upper rotation, posterior tilt, and external rotation in the shoulder and protects the subacromial space, (Ludewig et al, 2004), the weakness of this muscle can be related to shoulder pathologies (Tsai et al, 2003, Glousman et al, 1988).

On the other hand, electromyography analyzes showed that patients with Shoulder impingement has increased activity in the upper trapezius but decreased activity in the anterior teeth during arm elevation (Ekstrom et al, 2003). The increase in electromyographic activity in the upper trapezius can be a factor in the direction of anterior tilt and excessive scapular elevation and ultimately lead to the narrowing of the subacromial space. For this reason, maintaining the natural scapulohumeral rhythm requires exercises that balance the upper, middle, lower, and anterior trapezius (Ekstrom et al, 2003).

Generally, the active and balanced participation of the rotator cuff and scapulothoracic muscles is essential for producing efficient shoulder movements and girdle stability (Bertelli & Ghizoni, 2005). So that therapists suggest exercise programs based on this (Ballantyne et al, 1993). According to Glousman [11], electromyography studies have provided useful information to evaluate muscle activity and prepare exercise and rehabilitation protocols (Glousman, 1993). Although determining a suitable rehabilitation program for the shoulder complex is vital for the quick return of the patient to his profession and activity, and determining programs with the greatest benefit for specific patients with shoulder pathologies is one of the best treatment strategies, training recommendations to prevent shoulder pathologies, especially in athletes and people who use their upper limbs frequently, are more important. They are classified under[12].