Successful weaning from mechanical ventilation (MV) belongs to the challenges in critical care. The study evaluated the effect of the addition of in-bed leg cycling using a MOTOmed device to standard rehabilitation on the length of MV. Randomized open-label clinical trial. Sixty-seven mechanically ventilated patients were random allocated in the in-bed leg cycling MOTOmed group (m-group) and the control group (c-group). The standard physiotherapy was carried out twice a day in both groups. The m-group received additional in-bed leg cycling rehabilitation using a MOTOmed device once daily. We included 20 patients in m-group and 19 in c-group in the final analysis. In the m-group, a non-significant reduction in both total length of MV (21.0 ± 9.78 vs. 24.4 ± 10.88 days, p = 0.915) and length of MV from randomization (5.4 ± 6.17 vs. 8.7 ± 8.00 days, p = 0.860) was observed. Both groups had significant muscle strength improvement (knee joint extension, handgrip). However, the m-group patients reached the same muscle strength level in a shorter time (8.70 ± 6.44 vs. 6.8 ± 4.3 days, p = 0.534). In our study, adding the MOTOmed device in-bed leg cycling to standard rehabilitation did not significantly reduce mechanical ventilation length in critically ill patients.