Effects of mental fatigue on exercise intentions and behavior


Background: Exerting cognitive control results in mental fatigue, which is associated with impaired performance during physical endurance tasks. However, there has been little research on the effects of mental fatigue on people's perceptions or behaviors involving lifestyle or recreational exercise. Purpose: The purpose of this study was to examine the effect of mental fatigue on intended physical exertion and exercise performance reflective of current physical activity guidelines. Methods: Using a counterbalanced design, participants completed two 50-minute experimental manipulations (high vs. low cognitive control exertion) before exercising at a self-selected intensity for 30 minutes. At Visit 1, participants performed a graded exercise task to gain familiarity with a range of exercise intensities and rating perceived exertion (RPE) while exercising. At Visits 2 and 3, participants rated their intended RPE for the exercise session, performed the experimental manipulations, re-rated their intended RPE, and then completed 30-minutes of exercise on a cycle ergometer. Total work performed while exercising was recorded for each session. Results: Compared to the low cognitive control condition, the high cognitive control manipulation resulted in significantly greater mental fatigue (d = .73), significantly greater reductions in intended RPE (Mean difference = -0.62) and significantly less total work (-12.7 kJ) performed during the exercise session. Conclusions: Mental fatigue alters the amount of physical effort people are willing to invest in an exercise workout and follow through with those intentions by doing less work. These are the first results showing people may deliberately adjust their physical effort to cope with mental fatigue.

Acknowledgments: SSHRC; McMaster SSHRC Explore Grant