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


The beneficial effects of imagery on performance have been observed across many types of tasks yet, under certain conditions, imagery has been shown to negatively affect physical performances (Beilock et al., 2001).  Recently, Macrea et al. (2014) demonstrated that imagining oneself performing acts requiring self-control led to impairments in hypothetical task scenarios involving behavioural self-control.  Thus, imagery of physical tasks that require self-control may lead to suboptimal physical performance.  The purpose of this study was to investigate the aftereffects of performing imagery of a physically-effortful self-control task on actual performance of a physically-effortful self-control task and muscle fatigue.  Participants (N = 50) performed two isometric handgrip endurance trials (50% of maximum contraction) separated by either an imagery manipulation (n = 25) or a quiet rest period (n = 25).  The imagery manipulation had participants imagining performing an isometric handgrip task identical to the handgrip task they had performed on trial 1.  Forearm muscle activation (EMG) was monitored throughout the experiment.  Results showed the imagery group experienced greater negative changes in endurance performance from trial 1 to trial 2, F(1, 48) = 9.54, p = .003, d = 0.87, compared to controls.  Furthermore, the imagery group showed greater increases in EMG amplitude at baseline, F(1, 48) = 6.64, p = .01, d = 0.73, and at 25%, F(1, 48) = 4.62, p = .03, d = 0.61, of the second endurance trial compared to control participants.  The EMG results indicate greater motor unit recruitment by the imagery group despite task demands remaining constant.  These findings imply that self-generated imagery of an effortful physical task activates or depletes neural substrates causing muscle fatigue and impaired muscular endurance.  Findings have implications for the timing of imagery relative to endurance task performance, imagery content, and the type of imagery being performed.