Marvian Dwi Harjanto, and Gatot Jariono. “Method of Strengthening Arm Muscles Against the Ability of the Tennis Flat Service Stroke (Experimental Study in Students of Muhammadiyah University of Surakarta)”. International Journal of Educational Research &Amp; Social Sciences, vol. 2, no. 4, Aug. 2021, pp. 743-50, doi:10.51601/ijersc.v2i4.142.