We examined the ability of patients with spinal cord injury to undergo adaptations to chronic exercise training (cycle ergometry) invoked by functional electrical stimulation (FES) of the legs. Nine such patients performed incremental and constant work rate exercise before and after exercise training. Exercise sessions averaged 2.1 ± 0.4/wk, and consisted of 30 min/session of continuous FES recumbent cycling with increasing work rate as tolerated. Peak ˙VO2 and peak work rate significantly improved with training. Peak ˙VO2 was significantly correlated with peak heart rate both before and after training (r = 0.97 pre and 0.85 post, P < 0.01 for both). The time course of the˙VO2, ˙VCO2 and ˙VE responses to constant-load exercise (unloaded cycling) and in recovery (mean response time MRT) were very long prior to training, and became significantly faster following training. However, there was no correlation between percentage improvement in either MRTon or MRToff for ˙VO2 and the percentage increase in peak ˙VO2. Exercise tolerance in these patients with spinal cord injury appears to be a direct function of the ability to increase heart rate. Further, exercise training can elicit significant improvements in both exercise tolerance and in gas exchange kinetics, even when performed only twice per week. However, these improvements may be accomplished by different mechanisms.