High Mental Fatigue Magnitude Generates Greater Impaired Resistance Exercise Performance Than Moderate Mental Fatigue Magnitude in Trained Adults

Mental fatigue (MF) has been widely investigated in resistance exercise (RE). However, the results remain inconsistent, likely due to variability in the cognitive load across studies and, most importantly, the lack of individualized assessments of self-reported MF levels among participants before initiating the RE session. Therefore, the present study aimed to analyze the acute effect of different levels of MF induced by prior cognitive effort on the subsequent number of repetitions performed during an RE session. In a crossover trial, 20 participants were randomly assigned to three experimental conditions: a control and two mentally fatiguing conditions. In the MF conditions, the participants performed a computerized Stroop word-color (ST) task until reaching 40 mm (moderate MF) and 80 mm (high MF) on the visual analog scale for MF. Following all three conditions, participants completed an RE session consisting of six sets of half back-squat performed to muscle failure with a fixed load of ∼45% 1RM (1.0 m.s^-1). Physical and perceptual parameters-including total repetitions, repetitions per set, repetitions per velocity loss, and rating of perceived exertion (RPE)-were measured during the RE session. Participants exhibited a lower number of repetitions and a higher RPE during RE in the high MF condition compared to the moderate MF and control conditions, with a significant difference also observed between the moderate MF and control conditions (p < 0.05). In summary, these findings suggest that a high level of subjective MF results in a greater magnitude of impairment in physical performance during an RE session.