DOES PRIOR MENTAL FATIGUE AFFECT SUBJECTIVE MEASURES DURING AND AFTER A CYCLING TIME TRIAL?

BACKGROUND: Mental fatigue (MF) can manifest itself in a subjective, physiological and a behaviorally manner, and can negatively impact physical performance [1]. A multitude of studies have investigated perceived effort during exercise in a mentally fatigued state [1]. However, investigating additional subjective measures of fatigue during exercise is essential to understand how MF affects performance. Therefore, we aim to examine how MF affects perceived effort, mental and physical fatigue during a 15-minute cycling time trial in a mentally fatigued state. METHODS: Current results are part of an ongoing randomized cross-over trial. 51 participants (M/F=26/25; MeanAge =30 ± 8 y; BMI; 22.6 ± 2.5) visited the lab for three trials (familiarization, intervention and control). MF was induced with a 45-minute individualized STROOP task while the control trial consisted of watching a documentary. Directly after each condition, participants completed a 15-minute cycling time trial. The rate of perceived effort (0-100 RPE scale), physical fatigue and MF (0-100 scale) were monitored at the start, during (every 3 minutes) and at the end of the time trial. A two-way repeated measures (2x7) ANOVA was employed to test changes between conditions over time of each measure separately. Significant interaction effects were followed-up with paired T-tests. RESULTS: For perceived MF, an interaction between condition and time (F=15.5, P<0.001, effect size=0.237) and a main effect of condition (F=19.4, P<0.001, effect size=0.280) were found. At the start of the time trial, perceived MF was significantly higher in the MF condition vs. control condition (MF=36.5 ± 23.9; CON = 18.4 ±15.3; t=5.664; P<0.001). Between the start and 12th minute, perceived MF decreased in the MF condition (MeanDifference= -7.29) whereas an increase was found in the control condition (MeanDifference = 7.22). Perceived physical fatigue and effort increased over time for both conditions, but only physical fatigue revealed a main effect of condition with higher scores in the MF condition (F=4.2, P=0.046, effect size=0.820). CONCLUSION: Preliminary results show that a 45-min individualized Stroop task induced a higher MF perception before, during and after a 15-minute cycling time trial. In the MF condition, exercise decreased perceived MF over time, which reflects positive effects of exercise on MF. Physical fatigue was negatively affected by MF, possibly reflecting a separate working mechanism of MF on effort and physical fatigue perception. Future studies should further explore the underlying mechanisms of MF during exercise by relating subjective to physiological fatigue measures.