Mental training, as physical training, enhances muscle strength. Whereas the repetition of maximal voluntary contractions (MVC) induces neuromuscular fatigue, the effect of maximal imagined contractions (MIC) on neuromuscular fatigue remains unknown. Here, we investigated neuromuscular alterations after a mental training session including MIC, a physical training session including MVC, and a combined training session including both MIC and MVC of the elbow flexor muscles. Methods: Ten participants performed 80 MIC (duty cycle, 5-s MIC and 10-s rest), 80 MVC (identical duty cycle), or 80 MVC and 80 MIC (5-s MVC, 2-s rest, 5-s MIC, and 3-s rest) in three separate sessions. MVC torque was assessed five times over the course of the training and 10 min after the end of the training in the three protocols. Central activation ratio (CAR(c)), reflecting central fatigue, and corticospinal excitability, at rest and during MIC, were estimated using transcranial magnetic stimulation. Results: Both the physical training and the combined training induced an approximately 40% drop of MVC torque, accompanied with an approximately 10% decrease of CAR(c) without significant difference between the two sessions. On the contrary, the repetition of MIC did not reduce maximal force production capacity and did not alter CAR(c). Corticospinal excitability was always facilitated during MIC compared with that during rest, ensuring that the participants imagined the desired movement. Conclusions: These results suggested that one session of mental training alone or combined with physical training do not induce (additional) neuromuscular fatigue despite the repetitive activation of the corticospinal track. Motor imagery may be added to physical practice to increase the total workload without exacerbating neuromuscular fatigue.