Changes in the muscle performance of professional motorized athletes using pycnogenolcontaining supplements have not been clarified. The purpose of this study was to evaluate the changes in muscle strength and endurance of professional cyclists during 4 weeks of training with the use of PycnoRacer TM . [Participants and Methods] Eight professional cyclists were requested to consume PycnoRacer TM twice/day for 4 weeks. The muscle endurance test consisted of 50 consecutive knee flexion and extension exercises at 180°/sec using an isokinetic torque machine before and after PycnoRacer TM administration. The athletes' body composition, including leg muscle mass, was also measured. [Results] The maximum flexor muscle torque and 41st-50th flexion muscle torque values significantly improved after supplement consumption (average improvement of 8.5%; range, 13.3-67.2%). The leg muscle mass and body composition did not differ significantly between the two conditions. The participants showed an average improvement of 31.8% (range, 0.9-67.8%) in their total work with cycling training. No adverse events were observed. [Conclusion] The use of PycnoRacer TM may improve training, muscle strength, and endurance, but not muscle mass.