Vysotskaya, T., and S. Golubnichy. “Development of Special Endurance for Cross-Country Skiers of 15-17 Years Old”. Journal of Human Sport and Exercise, vol. 16, no. 2proc, Mar. 2021, pp. S212-S220, https://www.jhse.ua.es/article/view/2021-v16-n2-proc-development-special-endurance-cross-country-ski.