Physical Activity, Academic Stress, and Motivation in Physical Education: A Cross-Sectional Analysis by Sex and Grade Level. - León-Reyes BB; Galeano-Rojas D; Granados-Moreno M; de Souza-Lima J; Farías-Valenzuela C; Castillo-Paredes A; Valdivia-Moral P (Healthcare (Basel, Switzerland), 2026)