A Comparison Study on the Electrical Activity of Arm Abduction Muscles During Shoulder Abduction and Scaption Between Shooting Disciplines

* Corresponding Author: Seyyed Hossein Hosseini, PhD. Address: Department of Sports Pathology and Corrective Exercise, Faculty of Physical Education, University of Guilan, Rasht, Iran. Tel: +98 (919) 9196275 E-mail: hoseini.papers@gmail.com 1. Department of Sports Pathology and Corrective Exercise, Faculty of Physical Education, University of Guilan, Rasht, Iran. Safoura Heshmati1 , Hassan Daneshmandi1 , *Seyyed Hossein Hosseini1


Introduction
thletes in various sports need to perform continuous exercises and strengthen certain muscles of the body to achieve high levels of performance, and have to spend a lot of time training under the predominant physical condition of that sport. As a result, depending on the predominant condition of each sport, the level of muscle A activity affecting sports skills is affected [1]. Shooting is one of the most important sports competitions in the world such that the number of gold medals obtained in shooting competitions is equal to that in athletics and swimming competitions [2]. A review of previous studies shows that most researchers have examined shooting disciplines from various other aspects, including posture and postural deformities, musculoskeletal pain, and balance [3][4][5].
Considering the position that athletes use in different shooting disciplines, it seems that the deltoid and supraspi-natus muscles are involved in performing the movement, each of which has a relative role in each discipline. Moreover, due to the adaptive changes in posture, the position of shoulders may changes and therefore, it is expected that the activity of the muscles involved in sport performance will also change. By studying the electrical activity of muscles while identifying pathological stresses and adaptive muscle weaknesses due to specific shooting sports skills, it is possible to return the level of muscle activity to normal state with appropriate exercise interventions, and play an effective role in maintaining the physical health of athletes through training, prevention and treatment of such weaknesses. In this regard, the aim of this study was to compare the electrical activity of deltoid and supraspinatus muscles in two common positions used by shooters (abduction and scaption).

Methods
A total of 24 shooters (8 archers, 8 pistol shooters and 8 rifle shooters) participated in the study. They performed shoulder abduction and scaption movements up to 60 and 90 degree angles concentrically, and the electrical activity of deltoid and supraspinatus muscles was then recorded by surface Electromyography (EMG) using an 8-channel EMG device (MegaWin, Finland). The sampling frequency of EMG signals was set to 1000 Hz and the signal-to-noise ratio was 110 dB [6]. After getting familiar with the test and adapting the speed of elevation movement, the subject performed arm elevation movement in abduction plane with the dominant hand and external force.
First, MVIC tests were performed. Then the electrical activity of the deltoid and supraspinatus muscles was recorded during arm elevation in abduction and scaption planes at 60 and 90 degrees while holding a hand weight (5% of body weight) [7]. To analyze the data obtained from EMG, Megavin software and a 10-450 Hz band-pass filter were used [8]. To normalize the EMG signals, the RMS data of each muscle was divided by the MVIC of that muscle and then multiplied by 100. For this purpose, for each muscle, the maximum electrical activity was recorded in 5 seconds and it was used as a reference level for comparisons. Data were analyzed using one-way ANOVA and Tukey's test at the significance level of P<0.05.

Results
The results of this study show that the electrical activity of the anterior deltoid muscle at 60° abduction (P=0.018), 90° abduction (P=0.014) and 90° scaption (P=0.045) was significantly different between the archers and air pistol shooters; however, at 60° scaption (P=0.58), there was no significant difference between groups ( Figure 1). As can be seen in Figure 2, the activity of the middle deltoid muscle was significantly different only at 90° abduction (P=0.017) between the archery and air pistol groups. There was no significant difference between shooting groups at 90° scaption (P=0.14) and 60° scaption (P=0.31) states. There was also a difference between groups at 60° abducted position, but Tukey's test results showed that the difference was not significant (P>0.05). Figure 3 shows that in none of positions the posterior deltoid muscle activity was significantly different between shooting groups (P>0.05). Finally, according to Figure 4, supraspinatus muscle activity was significantly different between the archers and air pistol shooters at 90° abduction (P=0.007), but not at 60°abduction (P=0.055), 90° scaption (P=0.19) and 60° scaption (P=0.14) states.

Discussion
The results showed that the electrical activity of the anterior deltoid muscle in the abducted position and the activity of the middle deltoid and supraspinatus muscles only in the 90° abducted position were significantly higher in the archery group than in the air pistol group. The anterior deltoid muscle in archery is involved with the horizontal movement of the dominant arm. This muscle is not the main that causes horizontal abduction movement; hence, it is not appropriately strengthened in archery exercises. Previous studies have shown that the increased intensity of muscle activity can be due to its weakness and recall of more fibers [9]. The middle deltoid muscle in air pistol shooting, unlike other disciplines, is the active main muscle; hence, it is strengthened by long-term shooting training. Following the strengthening and increase of muscle strength due to repetition and training, its recall and activity also decrease [10].

Conclusion
The results of our study showed that the electrical activity of the posterior deltoid muscle in none of the conditions evaluated in this study was significantly different between the three shooting groups. Hence, it can be said that this muscle works equally in three shooting disciplines. On the other hand, this muscle has no role in shoulder scaption; hence, it cannot be expected that the level of activity in this position differs between the three groups. It seems that the level of supraspinatus muscle activity in 60° abducted posi-tion is almost the same between shooting groups. However, since the shoulder of dominant hand during air pistol shooting is abducted at 90 degrees, training and repetition in this position makes the muscle stronger at this angle and acts with less activity in this position.

Compliance with ethical guidelines
All ethical principles are considered in this article. The participants were informed about the purpose of the research and its implementation stages; they were also assured about the confidentiality of their information; moreover, they were free to leave the study whenever they wished, and if desired, the research results would be available to them. The consent form for participation and cooperation in the research was signed by all subjects.

Funding
The present paper was extracted from the MSc. thesis of the first author, Department of Sports Pathology and Corrective Exercise, Faculty of Physical Education, University of Guilan.

Conflicts of interest
The authors declared no conflict of interest.