Supported by University of Victoria Research Grant. The purpose of this investigation was to examine the influence of single leg training on one- and two-legged maximal oxygen consumption (VO2 max). Nine volunteers completed 7 weeks of one-legged interval training on a cycle ergometer adapted for single leg pedaling. The training regimen consisted of 15-20 intervals of 20 sec duration (1:3 work to rest ratio), 4 days a week at an intensity of 150% of the initial power output that elicited one-legged VO2 max. Pedaling cadence was maintained at 90 rpm. Heart rate (HR) was monitored throughout all training sessions. The results demonstrate that one-legged VO2 max was significantly increased (p < 0.05) from 3.36 l/min in the pretrained condition to 3.57 l/min and 3.69 l/min in the untrained (UT) and trained legs (T), respectively. No significant differences were observed between the UT and T legs for one-legged VO2 max after training. Two-legged VO2 max showed a 5% elevation following single leg training (p < 0.05). These data suggest that one-legged interval training of high intensity and short duration can improve both one- and two-legged maximal oxygen consumption. This finding implies that individuals can maintain aerobic power during rehabilitation following an injury to one limb, through the use of one-legged interval training on a cycle ergometer.J Orthop Sports Phys Ther 1988;10(1);8-11.