Maximal oxygen consumption (V_ O2max ) is impaired in heart (HTx), kidney (KTx), and liver (LTx) transplanted recipients and the contribution of the cardiovascular, central, and peripheral (muscular) factors in affecting V_ O2max improvement after endurance training (ET) has never been quantified in these patients. ET protocols involving single leg cycling (SL) elicit larger improvements of the peripheral factors affecting O2 diffusion and utilization than the double leg (DL) cycling ET. Therefore, this study aimed to compare the effects of SL-ET vs DL-ET on V_ O2max . We determined the DL-V_ O2max and maximal cardiac output before and after 24 SL-ET vs DL-ET sessions on 33 patients (HTx = 13, KTx = 11 and LTx = 9). The DL-V_ O2max increased by 13.8% 6 8.7 (p < 0.001) following the SL-ET, due to a larger maximal O2 systemic extraction; meanwhile, V_ O2max in DL-ET increased by 18.6% 6 12.7 (p < 0.001) because of concomitant central and peripheral adaptations. We speculate that in transplanted recipients, SL-ET is as effective as DL-ET to improve V_ O2max and that the impaired peripheral O2 extraction and/or utilization play an important role in limiting V_ O2max in these types of patients. Novelty: SL-ET increases V_ O2max in transplanted recipients because of improved peripheral O2 extraction and/or utilization. SL-ET is as successful as DL-ET to improve the cardiorespiratory fitness in transplanted recipients. The model of V_ O2max limitation indicates the peripheral factors as a remarkable limitation to the V_ O2max in these patients.
