Correlations among fatigue, respiratory function, balance and core muscle morphology in multiple sclerosis: a comprehensive observational study - De La Plaza San Frutos, Marta; Sanz-Esteban, Ismael; Salniccia, Federico; Bermejo-Franco, Alberto; García-Corona, Ameyalli; Palma-Baquedano, María Cristina; Castel-Sánchez, Marina; Estrada-Barranco, Cecilia (Frontiers in Neurology, 2025)