The Activation of Serratus Anterior Muscle During the Plank Exercise

Overview

Scapular dyskinesia is a condition characterized by changes in the resting position or movement of the scapula, which can impair shoulder function. Issues such as increased glenohumeral angle, reduced rotator cuff strength, and decreased subacromial space are commonly observed in athletes and sedentary individuals. Scapular muscle imbalances, particularly in the serratus anterior and lower trapezius muscles, are key contributors to dyskinesia. Studies show decreased EMG activity in these muscles among sedentary individuals, while increased activity is noted in overhead athletes. The relationship between serratus anterior activity and shoulder external rotation strength varies, highlighting the importance of strengthening scapular muscles to prevent injury in athletes. The core, including the spine, hips, pelvis, and abdomen, provides stability and transfers forces throughout the body. Core and scapular stability are interrelated, and impairment in scapular stability can weaken core strength, increasing the risk of injury. Therefore, exercises targeting both the core and scapular muscles are vital in athletic training programs. The plank exercise, which minimizes spinal load and promotes strength, is preferred for enhancing both core and scapular endurance. However, improper form, especially due to weak stabilizer muscles, can lead to compensations that increase injury risk, such as long thoracic nerve injury. Although studies exist on serratus anterior activity during plank exercises, there is limited research on its activation in athletes with scapular dyskinesia.

Scapular dyskinesia is defined as changes in the resting position of the scapula or in scapular movement. This condition can lead to negative changes in optimal shoulder function in individuals (Huang, Chen, Du, \& Lin, 2020; Jildeh, Ference, Abbas, Jiang, \& Okoroha, 2021). Changes such as an increase in the glenohumeral angle during horizontal abduction with scapular dyskinesia, a decrease in the maximal strength of the rotator cuff muscles responsible for compression stability, and a decrease in the subacromial space during overhead functions have been reported (Kibler \& Sciascia, 2019). These resulting functional impairments and imbalances are observed in 67-100% of athletes, as well as sedentary individuals, sometimes without symptoms and sometimes accompanied by shoulder pathology (Silva et al., 2022). While many factors contributing to the development of scapular dyskinesia have been identified, one key factor is scapular muscle imbalances. The scapulothoracic muscle groups frequently emphasized in relation to scapular dyskinesia are the lower trapezius and serratus anterior. The serratus anterior muscle is responsible for upward rotation, external rotation, and posterior tilt of the scapula. This muscle is crucial for maintaining normal alignment and the continuity of functional scapular movement (Ludewig, Cook, \& Nawoczenski, 1996; Ludewig \& Reynolds, 2009). In a study conducted with sedentary individuals, it was reported that the EMG activity of the lower trapezius and serratus anterior muscles decreased in the presence of scapular dyskinesia (Ann MJ Cools et al., 2014). In contrast to this study, the EMG activity of the serratus anterior muscle in overhead athletes with scapular dyskinesia was examined during various movement patterns and functions such as shoulder elevation, push-up exercises, and tennis serves. It was suggested that muscle activity increased compared to sedentary individuals, and this increase should be further investigated in the future (de Paula Marques \& Dionisio, 2024). Another point emphasized is the relationship between serratus anterior muscle activation and shoulder external rotation force in individuals with dyskinesia. While it has been stated that serratus anterior muscle activity decreases in the presence of scapular dyskinesia, external rotation muscle strength varies depending on the evaluated position. The importance of scapular muscles for shoulder external rotation strength has also been highlighted (Uga, Nakazawa, \& Sakamoto, 2016). Strengthening the muscles responsible for external rotation in overhead athletes and restoring normal scapular movement are key points that should be emphasized as a whole in injury prevention programs (Ann M. Cools, Johansson, Borms, \& Maenhout, 2015; Tooth et al., 2020). The core region of the body includes the spine, hips, pelvis, proximal lower extremities, and abdomen (Kibler, Press, \& Sciascia, 2006). The strength of these muscles allows for the transfer of compressive, translational, and shear forces, which serve to mechanically stabilize the spine and distribute forces to the rest of the body (Akuthota, Ferreiro, Moore, \& Fredericson, 2008; Fredericson \& Moore, 2005). Core stability is defined as the ability to control the position and movement of the trunk over the pelvis during integrated kinetic chain activities. It allows for the optimal transfer and control of force and movement to the terminal segment. Similar to the core muscles, the scapula plays an important role in transferring the force produced to the distal segments. Impairment in scapular stability can lead to a decrease in core strength, thereby increasing the risk of injury and reducing athletic performance. For this reason, exercises aimed at increasing scapular muscle and core endurance should be incorporated into athletes\' exercise programs to prevent injury and enhance performance (Cobanoglu, Keklik, Zorlular, Polat, \& Akaras, 2019). One of the exercises frequently included in Korean strength training programs for athletes is the plank exercise. Unlike sit-up exercises, the plank exercise is widely preferred to increase strength and endurance because it does not place a load on the lumbar spine and only minimally loads the spine when performed using body weight (Topçu et al., 2022). It is very important to perform plank exercises with correct segment alignment. The correct plank position is achieved in a push-up stance, with body weight supported by the forearms, elbows, and toes. The arms should be placed directly under the shoulder joints, and the entire body should maintain a straight alignment (Neporent, Schlosberg, \& Archer, 2011; Zhang, Dong, \& El Saddik, 2016). A lack of strength in the core or scapular stabilizer muscles during the plank may cause the person to adopt an incorrect posture by compensating with the thoracic spine or lower hips. In fact, a case report indicated that incorrect and excessive scapular activity during plank exercises may lead to long thoracic nerve injury (Güzel, Ozen, \& Sözay, 2023). There are studies in the literature examining the activity of the serratus anterior muscle, which is responsible for scapular stabilization, in athletes during plank exercises (Can, Harput, \& Turgut, 2024). However, no research has been found that evaluates serratus anterior EMG activity during plank exercises in athletes with scapular dyskinesia.\"