To determine whole-body energy and nitrogen responses to submaximal exercise during repletion levels of intravenous feeding (IVF), five normal male volunteers were hospitalized and underwent serial changes in nutritional intake consisting of weight-maintaining oral feeding (4 d), starvation (10 d), and weight-increasing parenteral feeding (10 d). Twelve-hour aliquots for urinary nitrogen, creatinine, and 3-methylhistidine were collected during the final 36 h of oral feeding and IVF. During these experimental periods, indirect calorimetry was utilized to determine resting oxygen consumption and that occurring during a 1-h period of submaximal (40% of maximal) upright, bicycle exercise. Despite differences in the route of nutrient delivery, oxygen uptake during a fixed rate of exercise (75 W) was similar during oral (16.7 +/- 0.4 mL X kg-1 X min-1) and IVF (14.7 +/- 1.0 mL X kg-1 X min-1). When compared with basal urinary losses, submaximal exercise resulted in diminished nitrogen (p less than 0.01, oral) and 3-methylhistidine (p less than 0.05, oral; p less than 0.01, IVF) excretion during a 12-h post-exercise recovery period.