The first aim was to examine in older adults the acute physiological effects of eccentric exercise (i.e. downhill treadmill walking, DW: -10% gradient, 30-min) at a self-selected walking speed. The secondary aim was to examine in older adults the effects of a 12-week concentric (level treadmill walking, LW: 0% gradient) and eccentric (downhill treadmill walking, DW: -10% gradient) endurance exercise intervention (30-min, 3x week) at a self-selected walking speed (SSWS, re-evaluated every 4-weeks) on the functional and physiological adaptations. Participants were randomly assigned to an exercise group (LW: 0=13 or DW: n=IS). Eighteen participants (8 LWand 10 DW) completed the 12-week intervention. Wearing the Cosmed K4b2 portable metabolic system had no effect on performance and physiological responses during the I-mile Rockport Fitness Walking Test (Study I)...