Trombetti A, Hars M, Hsu FC, Reid KF, Church TS, Gill TM, King AC, Liu CK, Manini TM, McDermott MM, Newman AB, Rejeski WJ, Guralnik JM, Pahor M, Fielding RA. Effect of Physical Activity on Frailty: Secondary Analysis of a Randomized Controlled Trial. Ann Intern Med. 2018 03 06; 168(5):309-316.