Objectives For several decades, a growing number of studies have highlighted that imagery-based suggestions, can efficiently influence motor control and perception. In the present study, we tested whether imagery-based suggestions without hypnotic induction might influence physical resistance performance and effort perception in the context of French firefighters’ usual training. Methods A group of 18 male firefighters had to keep the wall-sit posture as long as they could while listening to different scripts. In the first condition, imagery was related to Lightness. In the second one, it was related to Heaviness. In the Control condition, they just had to listen and pay attention to series of two-digit numbers. Results Results showed that the participants kept the posture longer in the Lightness condition than in the Heaviness one. Furthermore the effort was perceived as less difficult in the Lightness condition in comparison to the Heaviness and the Control ones. Moreover in the Lightness condition, the higher the participants scored in visual and kinesthetic imagery tasks (MIQ-R), the less they rated the exercise as difficult. Conclusions Imagery-based suggestions significantly influenced both physical resistance performance and effort perception without any prior hypnotic induction. Further studies are necessary to better understand the factors that modulate this influence.