BACKGROUND: To carry out their victim rescue and fire-fighting missions, firefighters perform high levels of physical exertion and among them strenuous muscular activity. A specific mental preparation protocol that could induce better strength performance throughout their 24-hour schedule is a major issue for firefighters. OBJECTIVE: This case report aims to examine whether a 6-minute Intervention combining mental imagery practices and breathing exercises, specifically designed to be used while travelling between the fire station and the mission site, would be able to promote maximum strength performance.

METHODS: A series of three Single Case Experimental Designs (SCED) was conducted in single blind design to investigate the effects of repeated challenge-withdrawals between the Intervention and the Baseline on the maximum voluntary isometric contraction (MVIC) strength of the hand-grip. RESULTS: Data analyses revealed that 62.5% to 100% of the hand-grip strength values during the Intervention periods were greater than or equal to the maximum data point recorded in the Baseline periods. The effect sizes of these highlighted increases of the hand-grip strength performance revealed by the percentage of non-overlapping data (PND) were 75% i.e., moderately effective on average. CONCLUSIONS: Such a "psyching-up" practice before an upcoming muscular activity can promote muscular strength in firefighters. These results have led French firefighter departments to integrate the teaching of these practices into the initial instruction of firefighters, and remains to be confirmed by a randomised control trial.