Effects of mental fatigue on exercise intentions and behaviour

Abstract

Exerting cognitive control results in mental fatigue, which is associated with impaired performance and increased perceived exertion during physical endurance tasks. However, there has been little research on the effects of mental fatigue on people's performance or perceptions about engaging in lifestyle exercise. 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. Using a randomized, counterbalanced design, participants completed two 50-minute experimental manipulations (high vs. low cognitive control exertion) before exercising. At Visit 1, participants performed a graded exercise task to familiarize them with a range of exercise intensities and their corresponding ratings of perceived exertion (RPE). At Visits 2 and 3, participants reported their intended RPE for 30-minutes of self-paced, cycling exercise, performed the experimental manipulations, re-rated their intended RPE, and then completed 30-minutes of exercise. Total work and average heart rate (HR) were recorded during each exercise session. High cognitive control exertion resulted in significantly greater mental fatigue (d = .73) and significant reductions in intended RPE (Mean difference = -0.62). Participants also performed less total work (-12.7 kJ) at lower average HR during exercise (-7.5 bpm) in the high cognitive control condition. Results suggest 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 University Arts Research Board Grant