Sugiarto , Aas, et al. “The Relationship Of Waist Flexibility Towards Smash Skills In Volley Ball Extracurricular Athletes In Sma N 13 Bengkulu Utara”. Sinar Sport Journal, vol. 1, no. 1, June 2021, pp. 1-3, doi:10.53697/ssj.v1i1.66.