O3‐09‐01: PROTECTIVE EFFECT OF PHYSICAL ACTIVITY ON LONGITUDINAL COGNITIVE DECLINE AND NEURODEGENERATION IN CLINICALLY NORMAL OLDER ADULTS WITH ELEVATED β‐AMYLOID BURDEN. (1st July 2019) - Rabin, Jennifer S.; Klein, Hannah; Kirn, Dylan; Schultz, Aaron P.; Yang, Hyun-Sik; Hampton, Olivia; Jiang, Shu; Buckley, Rachel F.; Viswanathan, Anand; Hedden, Trey; Pruzin, Jeremy J.; Yau, Wai-Ying; et al.