This study aimed to explore the effects of mental fatigue (MF) induced by an incongruent Stroop task (ST) and by using social media (SM) compared to watching a documentary (control) on dynamic resistance training. Twenty-one resistance-trained males attended three identical experimental sessions with the only difference of the randomized cognitive task (ST, SM, or control). Each session consisted of (a) baseline MF and motivation visual analogue scale responses, (b) cognitive task, (c) postvisual analogue scale responses, (d) warm-up, and (e) resistance training based on three sets of bench press at 65% of one-repetition maximum till concentric failure. Number of repetitions, ratings of perceived exertion, mean velocity of repetitions, and three repetitions in reserve estimated by subjects were recorded for each set. Both ST (p < .001) and SM (p = .010) effectively induced MF, but only ST impaired the number of repetitions performed in Set 2 (p = .036) and generated higher-than-normal levels of ratings of perceived exertion even reaching significant differences compared to SM in Set 1 (p = .005). However, SM also affected neuromuscular performance by impairing movement velocity in Set 1 (p = .003). The ability of estimating three repetitions in reserve or motivation was not affected by any condition (p range = .362-.979). MF induced by ST impaired the number of repetitions performed, what seems to be mediated by higher-than-normal levels of ratings of perceived exertion. Besides, SM also impaired the ability to apply force against 65% of one-repetition maximum measured by movement velocity.
Keywords: cognitive exertion; ego depletion; physical performance; resistance exercise; strength endurance performance.