Marcora et al. 2009, Mental fatigue impairs physical performance

Randomised crossover (n=16): 90 minutes of demanding cognitive work before cycling cut time to exhaustion by about 15% compared with a control task, with no difference in cardiorespiratory or metabolic responses. The effect was mediated by higher perceived exertion, the central evidence for the psychobiological model in which endurance is limited by perception of effort rather than a physiological ceiling. Moderate (influential framework, still contested against physiological-limit accounts).