Exercise standards for testing and training - Fletcher, G F; Ades, P A; Kligfield, P; Arena, R; Balady, G J; Bittner, V A; Coke, L A; Fleg, J L; Forman, D E; Gerber, T C; Gulati, M; Madan, K; Rhodes, J; Thompson, P D; Williams, M A (Circulation, 2013)