Effect of power training on function and body composition in older women with probable sarcopenia. A study protocol for a randomized controlled trial - Luis Polo-Ferrero; Susana Sáez-Gutiérrez; Arturo Dávila-Marcos; Fausto J. Barbero-Iglesias; María C. Sánchez-Sánchez; Ana Silvia Puente-González; Roberto Méndez-Sánchez (PLoS ONE)