Patients undergoing intensive chemotherapy for acute leukaemia or aggressive lymphoma not only suffer from the direct side effects of chemotherapy such as infections due to long-lasting immuno-suppression and aplasia, but also from marked fatigue and the inability to do normal physical activity. Furthermore, especially in patients with severe thrombocytopenia, anaemia and leukopenia, doctors recommend abstaining from physical exercise due to the risk of potential bleeding and tissue damage. The normally recommended cutoff level to perform exercise is 50,000 platelets per microliter or haemoglobin of 8 g/dl. This leads to a vicious cycle of losing physical strength and muscle with subsequent development of treatment-related cachexia and an increased treatment mortality. As number of publications focus on the importance of physical exercise in patients with solid tumours, increasing evidence is found that suggests positive effects on major clinical endpoints such as rate of infection, quality of life and even relapse rate and overall survival. With this work, we intended to address whether intense supervised ergometer training is feasible in patients with severe pancytopenia and whether it has any effect on patients undergoing high-dose chemotherapy. Furthermore, this study was initiated as the groundwork for a large phase III randomised trial.