Network Physiology in Aging and Frailty: The Grand Challenge of Physiological Reserve in Older Adults - Romero-Ortuño, Román; Martínez-Velilla, Nicolás; Sutton, Richard; Ungar, Andrea; Fedorowski, Artur; Galvin, Rose; Theou, Olga; Davies, Andrew; Reilly, Richard B; Claassen, Jurgen; Kelly, Áine M; Ivanov, Plamen Ch. (Frontiers in Network Physiology, 2021)