International Journal of Human Movement and Sports Sciences 9(3): 543-553, 2021 http://www.hrpub.org DOI: 10.13189/saj.2021.090321 Reliability of Testing of the Electrical Activity of Muscles during Isometric Contractions in Archery Ihor Zanevskyy 1,* , Romana Sirenko 2 , Oksana Shukatka 2 , Natalia Bashavets 3 , Ivan Rybchych 4 1 Department of Informatics and Kinesiology, Lviv State University of Physical Culture, Lviv, 79007, Ukraine 2 Department of Physical Education and Sports, Ivan Franko Lviv National University, Lviv, 79000, Ukraine 3 Institute of Physical Education, Sports and Rehabilitation, South Ukrainian National Pedagogical University named after KD Ushynsky, Odesa, 65000, Ukraine 4 Department of Sport Medicine, Human Health, Lviv State University of Physical Culture, Lviv, 79007, Ukraine Received February 5, 2021; Revised April 29, 2021; Accepted May 16, 2021 Cite This Paper in the following Citation Styles (a): [1] Ihor Zanevskyy, Romana Sirenko, Oksana Shukatka, Natalia Bashavets, Ivan Rybchych , "Reliability of Testing of the Electrical Activity of Muscles during Isometric Contractions in Archery," International Journal of Human Movement and Sports Sciences, Vol. 9, No. 3, pp. 543 - 553, 2021. DOI: 10.13189/saj.2021.090321. (b): Ihor Zanevskyy, Romana Sirenko, Oksana Shukatka, Natalia Bashavets, Ivan Rybchych (2021). Reliability of Testing of the Electrical Activity of Muscles during Isometric Contractions in Archery. International Journal of Human Movement and Sports Sciences, 9(3), 543 - 553. DOI: 10.13189/saj.2021.090321. Copyright©2021 by authors, all rights reserved. Authors agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Abstract BACKGROUND. The archery sport needs a high level of accuracy and coordination between muscle forces. Electromyography is a useful and effective method in studding the electrical activity of muscles in archery. Resulting in a great variation in EMG data repeatability, the results regarding a theory of test reliability should be studied. PURPOSE. The research aims to develop a method of determination concerning reliability of testing of the electrical activity of muscles during isometric contractions in archery. METHODS. The electrical activity of rectus femoral muscle during isometric contractions with the maximal effort in bending of a thigh from −15º to 70º is tested in a sample of twenty skilled male archers of 23–28 years old. ANOVA for repeated measures, ICC and regression models are used. RESULTS. The electrical potential is found to be maximal (7.15 mV), when the joint angle equals −8.9º and minimal (1.44 mV), when the joint angle equals 62.8º. A ratio of sum of squares due interaction between subjects’ and joint angles’ variability to the total sum of squares variability of all measures is accepted as a measure of the error in a hypothetical function of dependence of the electrical activity of muscles on joint angles (23.3%, p < 0.001). A single measure test after elimination of trends in test–retest results shows a sufficient level of reliability: ICC(1,1)=0.745. Corresponding mean scores reliability of the test with five trials is estimated as good: ICC(1,k)=0.936, (k = 5). CONCLUSION. A method of determination concerning reliability of testing of the electrical activity of muscles during isometric contractions specifically to the archery sport is recommended to the practical employment. Keywords Archery, Electromyography, Reliability, Modeling 1. Introduction The archery sport needs a high level of accuracy and coordination between muscle forces. Specifically, postural stability is required and should be obtained with antagonistic equilibrium of lower extremity and trunk muscles. In this area, Sarro, Viana, and De Barros [1] investigated correlation between postural stability and consistent of arrow hits at the archery target. The main attention regarding scientific research of muscle interaction in archery is given to the upper limbs, specifically to muscles of a forearm. In measuring electrical activity in the forearm muscles (flexor digitorum superficialis, extensor digitorum, deltoid, and trapezius), Tinazci [2] surface electromyography techniques were used. Surface EMG is recognized as a reliable and