Optimal cognitive and motor performance relies on the ability to prepare and execute responses with precise timing. Autonomic arousal is thought to modulate these processes, influencing both the readiness and execution phases of actions. This study explores the effects of motor imagery-based mental training on reactive inhibitory control and its correlation with autonomic activity. In Experiment 1, 20 healthy participants completed a stop-signal task to enable the evaluation of motor response performance. The results showed that mental training led to significant improvements in overall response speed and stop-signal reaction time, indicating enhanced reactive inhibition, particularly during the diastolic phase. This suggests an interaction between training effects and the cardiac cycle. In Experiment 2, 20 healthy participants performed an alertness task with two foreperiods (650 ms and 710 ms) to enable the assessment of response timing with different preparatory intervals. Mental training significantly improved response timing during the longer foreperiod, and this enhancement correlated with increased parasympathetic activity. Similarly, an improvement in the suppression of premature responses was observed during the shorter foreperiod, although it did not reach statistical significance after correction. A significant reduction in omission rates in trials without foreperiods was also found. These findings suggest an association between mental training, temporal preparation, and autonomic modulation. However, further research is needed to determine the nature of this relationship and its underlying mechanisms.