The purpose of this study was to compare the oxygen uptake and heart rate responses during submaximal arm cranking to combined arm cranking+electrical stimulation (ES)-induced leg cycling in individuals with spinal cord injury (SCI). Seven subjects with paraplegia (T 4 ± T 12 ) performed combined arm and leg cycling exercise for 5 min, followed by arm cranking alone at the same power output for a further 5 min. During both exercise conditions, steady state oxygen consumption (VO 2 ), carbon dioxide output (VCO 2 ), expired ventilation (V E ) and heart rate (HR) were determined. The respiratory exchange ratio (RER) and oxygen pulse were calculated from the measured variables. During combined arm+electrical stimulation-induced leg cycling exercise, the VO 2 was 25% higher (1.58 l min 71 vs 1.26 l min
71), but the HR was 13% lower (132 b min 71 vs 149 b min 71 ), than during arm cranking exercise alone. Oxygen pulse and VCO 2 were also signi®cantly higher (by 42% and 25%, respectively) during combined arm+ES-induced leg exercise, but there were no dierences between the two exercise conditions for V E or RER. These data suggest that the absence of the leg`muscle pump' and a reduced venous return of blood to the heart elevate exercise heart rates during submaximal arm cranking. Conversely, combined arm cranking+ES-induced leg cycling exercise provides the body with a greater metabolic stress than arm cranking alone, while reducing the cardiac stress. The mechanism explaining the heart rate response, however, remains unclear, but may have been in¯uenced by the blood pressure variations across the range of lesions. The ®ndings from this study may have implications for the relative bene®t of combined arm+ES-induced leg cycling training for people with paraplegia.