Backward running has long been used in sports conditioning programs and has recently been incorporated into rehabilitative settings as a method of increasing quadriceps strength while decreasing the joint compressive forces about the knee. Although backward locomotion has been studied kinetically, the metabolic cost of backward walking and/or running has not to our knowledge been previously characterized. Oxygen consumption and other cardiopulmonary variables were measured under constant speed exercise during backward and forward walking at 107.2 m·min−1 and during backward and forward running at 160.8 m·min−1. Peak oxygen consumption (JOURNAL/mespex/04.02/00005768-199401000-00019/ENTITY_OV0312/v/2017-07-20T222405Z/r/image-pngO2peak) was also measured during maximal incremental backward and forward running. JOURNAL/mespex/04.02/00005768-199401000-00019/ENTITY_OV0312/v/2017-07-20T222405Z/r/image-pngO2, HR, and blood lactate were significantly higher (P < 0.001) during backward walking and running than during forward walking and running. During backward walking and backward running, subjects exercised at 60% and 84% of their forward JOURNAL/mespex/04.02/00005768-199401000-00019/ENTITY_OV0312/v/2017-07-20T222405Z/r/image-pngO2peak, respectively. In conclusion, for a given speed, backward locomotion elicits a greater metabolic demand and cardiopulmonary response than forward locomotion. In general, these data suggest that while undergoing rehabilitation, an injured athlete may continue to exercise using backward walking/running at an intensity sufficient enough to maintain cardiovascular fitness levels.