Perceived effort in force production as reflected in motor-related cortical potentials

Objective: The perceived effort in force production was investigated in a series of experiments where subjects performed isometric force tasks with the index finger while the nominal force, the rate of force development and signal gain were controlled and rating of effort for each task was obtained. The hypotheses tested were that: (1) force-related perceived effort may selectively influence the amplitude of motor-related cortical potentials (MRCP); and (2) the MRCP may directly reflect the intensity of perceived effort associated with force production. Methods: The force trace was displayed on a computer monitor using various control-gains so that the perceived effort matched or was at odds with actual muscular effort applied to the load cell to accomplish the task. The MRCP were extracted from continuous EEG records using averaging techniques. Results: The findings showed that: (1) perceived effort proportionally increased with the increment of rate of force development and force error, but not with the actual force level; (2) the amplitude of the MRCP increased when a large amount of force was accompanied by an increased rate of force development; (3) the amplitude of early components of MRCP preceding the force initiation (MP-100 to 0) increased as a function of anticipated effort, whereas, the amplitude movement-monitoring potentials (MMP) accompanying the force production increased as a function of actual force level. Conclusions: The findings from this study provide additional insight clarifying the distinct patterns of EEG activity exhibited under various degrees of perceived effort associated with force output. The findings support the hypothesis that the early components of MRCP may reflect the perceived effort associated with achieving the required force level. Significance: The results from this study may be considered in the larger context of physical activity in terms of importance of perceived effort during prescribed exercise in rehabilitation programs.