Author(s): DE LIMA JUNIOR, D., FROTA-JUNIOR, L.J.S., FORTES, L.S., VASCONCELOS, G., ABASRASHID, N., BARTOLOMEI, S., MARCORA, S.M., Institution: ECAMPUS UNIVERSITY, Country: ITALY, Abstract-ID: 1948

INTRODUCTION:
The harmful effects of mental fatigue (MF) on resistance exercise (RE) have become a growing field of interest. The recent increase in randomized clinical trials (RCTs) evaluating the effects of MF on RE warrants a 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 summarize the effects of MF on RE volume [i.e., number of repetitions, and total training volume load (TTV; number of repetitions x number of sets x load)] in healthy individuals, comparing cognitive task interventions (e.g., STROOP, PVT, AX-CPT, social networks, video games) with controls (e.g., documentary). The results may clarify whether cognitive effort should be avoided before RE sessions since reduced volume could hinder long-term adaptations (e.g., hypertrophy). Thus, the research question for this systematic review was: Does MF induced by previous cognitive effort reduce subsequent RE volume in apparently healthy adults?
METHODS:
A systematic search was conducted using PubMed, Web of Science (WoS), SPORTDiscus, Scopus, and PsycINFO. Only randomized controlled trials involving healthy human participants, a central executive task requiring cognitive effort, an easier cognitive comparison task, and an RE performance task (e.g., number of repetitions and total training volume load) were included.
RESULTS:
A total of 10 studies provided 13 comparisons with more than 185 participants, providing data with a moderate level of evidence. The random-effects meta-analysis revealed a significant mean negative effect of prior cognitive effort on RE volume (g = -0.35). Subgroup analysis showed significant differences between MF and control conditions for multi-joint exercises (p < 0.00001), but not for single-joint exercises (p = 0.09). A greater magnitude of negative effect was observed for moderate-intensity RE (g = -0.56) when compared to low (g = -0.31), high (g = -0.25), and body-weight (g = -0.25) exercises.
CONCLUSION:
The main analysis results showed that exposure to a cognitively demanding task has a significant, small negative effect on subsequent physical performance (g = − 0.35; 95% CI = −0.50, −0.21; p < 0.00001), without significant heterogeneity in the data (p = 0.10 and I2 = 36%). Also, GRADE analysis gathered the available evidence about the effects of MF on RE volume. Overall, the quality of evidence, as assessed by GRADE, was moderate, indicating moderate confidence in the correlation between true and estimated effects. To contextualize these findings for applied practice, the observed effect sizes translate to meaningful reductions in training volume that may compromise both acute workout quality and potentially long-term adaptations. Thus, based on these findings, strength and conditioning professionals should implement evidence-based strategies to mitigate mental fatigue effects on resistance training quality.