TY JOUR TI DEVELOPMENT OF ENDURANCE IN SENIOR SCHOOLCHILDREN BY THE METHOD OF USING SPECIAL RUNNING EXERCISES KW endurance KW senior schoolchildren KW special cross-country KW exercises KW training sessions KW physical culture JO Scientific notes of P. F. Lesgaft University AU Kryukova, S.P. AU Ryabchuk, V.V. PY 2023 IS 0 PB National State University of Physical Education, Sports and Health named after P.F. Lesgaft