A prospective study of walking as compared with vigorous exercise in the prevention of coronary heart disease in women. - Manson,J.E.; Frank,B.H.; Rich-Edwards,J.W.; Colditz,G.A.; Stampfer,M.J.; Willet,W.C.; Speizer,F.E.; Hennekens,C.H. (N Engl J Med, 1999)