Acute Effects of Contract–Relax PNF With and Without Neuromuscular Electrical Stimulation on Hamstring Flexibility and Jump Performance in Adolescent Soccer Players: A Randomized Controlled Trial - Carlos Salvador-Huerta; Pedro Azanon-Nogueira; Eloi Suárez-Pazos; Valeria Betancourt-Cabeza; Irene Lazcano-Nogueira; Andrea Porcu; Ángel Manuel de la Hera-Sastre; Juan J. Amer-Cuenca; Juan Francisco Lisón (International Journal of Sports Physical Therapy, 2026)