It wears me out just imagining it! Mental imagery leads to muscle fatigue and diminished performance of isometric exercise.

The purpose of this study was to investigate the aftereffects of self-generated mental imagery of an effortful task on physical self-control endurance and muscle fatigue. Participants performed two isometric handgrip endurance trials (50% of maximum contraction) separated by either an imagery manipulation or a quiet rest period. The imagery group showed greater negative changes in endurance performance from trial 1 to trial 2 (p=.003, d=0.87) and increased muscle activation at baseline (p=.01, d=0.73) and at 25% (p=.03, d=0.61) of the second endurance trial compared to controls. We conclude that imagined performance of an effortful task depletes self-control strength and contributes to muscle fatigue.