Few studies have thoroughly examined metabolic, cardiovascular, and psychophysiological responses to negative treadmill (TM) exercise. We compared oxygen consumption (VO2), heart rate (HR), and perceived exertion (RPE, 0-10 Borg scale) during incremental TM exercise featuring both downhill and uphill stages. Subjects were aerobically trained males (N = 12, VO2max = 61 ml.kg-1.min-1) and females (N = 12, VO2max = 53 ml.kg-1.min-1). On separate occasions, each subject walked (4.8 kph) or jogged (9.6 kph) for 25 min. Five minutes were spent at each of five grades (-10, -5, 0, 5, 10%, or the reverse). TM speed and percent progressions were randomized. VO2 and HR did not differ in the 4.8 kph condition when TM grade was negative. During 9.6 kph, both VO2 and HR significantly (P less than 0.001) increased with progressive increments, but increases were less when TM grade was negative. RPE did not differ in the 4.8 kph condition except at 10% grade, where responses were significantly (P less than 0.001) higher. In 9.6 kph, RPE responses were significantly (P less than 0.001) greater during positive stages. The only gender effect occurred at 10% in the 9.6 kph condition, where women had greater (P less than 0.01) RPE responses than men. Results suggest that both walking and jogging economies differ between negative and positive TM grades. Gender differences appear negligible when comparing aerobically trained men and women.