Background: There is growing evidence that chronic exercise is a promising intervention for combating feelings of low energy and fatigue. Although groups with well-defined medical conditions (for example cancer and heart disease) or unexplained fatigue syndromes consistently have reported improved feelings of energy and fatigue after chronic exercise, relatively few exercise training studies have been conducted with people who report persistent fatigue yet neither have a medical condition nor reach diagnostic criteria for an unexplained fatigue syndrome. The purpose of this investigation was to use a randomized controlled design to examine the effects of 6 weeks of chronic exercise training on feelings of energy and fatigue in sedentary, healthy young adults reporting persistent fatigue. Methods: Thirty-six healthy, young adults who reported persistent feelings of fatigue were randomly assigned to a moderate-intensity exercise, low-intensity exercise or no treatment control group. Participants in each condition then visited the exercise laboratory on 18 occasions over a 6-week period. Exercise laboratory visits occurred 3 days per week. Vigor and fatigue mood state scores were obtained at the beginning of the third exercise session each week for 6 weeks. Aerobic fitness was measured before and after intervention. Results: The effect of 6 weeks of exercise training on feelings of fatigue was dependent on exercise intensity; however, the effect on feelings of energy was similar for both the low- and moderate-intensity conditions. The changes in feelings of energy and fatigue were independent of changes in aerobic fitness. Conclusions: Six weeks of low and moderate exercise training performed by sedentary adults without a well-defined medical condition or an unexplained fatigue syndrome but reporting persistent feelings of fatigue resulted in similarly beneficial effects on feelings of energy. The effects for symptoms of fatigue were moderated by exercise intensity, and the more favorable outcome was realized with low-intensity exercise. Changes in feelings of energy and fatigue following exercise training were unrelated to changes in aerobic fitness.