Mental fatigue impairs strength endurance performance in trained individuals

Purpose Evidence of mental fatigue (MF) effects on dynamic strength performance and psychological responses is scarce and controversial. Thus, we examined whether highly demand cognitive task-induced MF influenced dynamic strength endurance performance and psychological responses to exercise. Methods After familiarizations with standardized protocols and procedures, 12 strength-trained individuals (24 ± 6 years; 1.77 ± 0.04 m; 79.0 ± 14.7 kg) completed two experimental trials in a randomized, crossover counterbalanced fashion. In each trial, participants performed a 5-set dynamic strength endurance test at 70% of one-repetition maximum load in bench press exercise, interspersed by 2 min. Before the strength endurance test, participants either performed a 30 min cognitive task (i.e. MF trial) or sat quietly (i.e., control trial—CON) for equal time. The total number of repetitions and psychological responses such as motivation, emotional arousal, affect, and ratings of perceived exertion (RPE) were obtained throughout the exercise protocol. Results MF impaired the total number of repetitions ( p = 0.042; ES = 0.17; − 4 ± 5 repetitions; − 5.9 ± 11.9%) compared to CON. However, comparable psychological responses were observed between MF and CON trials in motivation, emotional arousal, affect, and RPE (all comparisons, p > 0.05). Conclusions These results have important implications for exercise training and performance assessment in both athletic and clinical populations aiming at increases in muscle strength and hypertrophy in response to strength training.