['Walking is usually undertaken at a speed that coincides with the lowest metabolic cost. Aging however, alters the speed-cost relationship, as preferred walking speeds decrease and energy costs increase. It is unclear to what extent this relationship is affected when older women undertake walking as an exercise modality. The aim of this study was to compare the energetic cost of walking at a self-selected exercise pace for a 30 minute period in older and younger women.', "The energetic cost of walking was assessed using the energy equivalent of oxygen consumption measured in 18 young (age 25 to 49 years) and 20 older (age 50 to 79 years) women who were asked to walk at their 'normal' exercise pace on a motorized treadmill for 30 minutes duration.", 'The mass-specific net cost of walking (Cw) was 15% higher and self-selected walking speed was 23% lower in the older women than in the younger group. When speed was held constant, the Cw was 0.30 (J.kg-1.m-1) higher in the older women.'] Is walking speed at self-selected exercise pace lower but energy cost higher in older versus younger women?