To assess the value of exercise training after traumatic brain injury (TBI), 14 sedentary adults with TBI performed a supervised circuit training program three times per week for 16 consecutive weeks. The program was designed to include equal volumes of both aerobic and neuromuscular training to increase the subjects' oxidative capacity and simultaneously improve their locomotor efficiency. Before and after the experimental training program, height, weight, blood pressure, skinfold thickness, grip strength, abdominal muscular endurance, and submaximal and peak rates of oxygen consumption were measured, and the index of physiological fatigue was calculated. The TBI patients manifested subnormal oxidative capacities and above-average oxygen costs locomotion. A 16-week circuit training program of moderate intensity and prolonged duration increased their oxidative capacity (p less than .01) and abdominal muscular endurance (p less than .01), but failed to reduce their oxygen cost of walking. Moderate and prolonged activity seems beneficial in the comprehensive rehabilitation of patients with TBI. The index of physiologic fatigability seems to be useful for the assessment, evaluation, and vocational placement of individuals with TBI.