Mental Fatigue and Resistance Exercise: A Systematic Review and Meta-Analysis Including GRADE Qualification

The recent increase in randomized controlled trials evaluating the effects of mental fatigue (MF) on RE warrants an update of the available meta-analytical evidence. This study presents the results of a comprehensive systematic review and meta-analysis, including GRADE qualification, examining the effects of MF on RE across different subgroups. We included only randomized controlled trials involving healthy human participants, a high-demand cognitive task requiring cognitive effort (e.g., Stroop test), a low-demand or passive control condition (e.g., watching documentaries), and a resistance exercise performance task assessing volume. A total of 11 studies reported 14 comparisons involving more than 205 participants, providing moderate-level evidence. The random-effects meta-analysis revealed a significant mean negative effect of cognitive effort on RE volume (g = -0.39 and p < 0.01). Subgroup analyses suggested that multijoint exercises may be more susceptible to impairment (g = -0.45 and p < 0.01) than single-joint exercises (g = -0.20 and p = 0.09). The magnitude of impairment appeared larger at moderate-intensity loads (60%-79% 1RM and g = -0.56) relative to low-intensity (g = -0.40) and bodyweight conditions (g = -0.25). Similarly, the effect appeared greater in high training volume conditions (g = -0.54) compared to moderate volume (g = -0.37). Overall, although this review confirms the negative impact of MF on RE volume, the findings should be interpreted with caution due to low-quality evidence.