Science says your mind gives up before your body.

Marcora believes that this limit is probably never truly reached—that fatigue is simply a balance between effort and motivation, and that the decision to stop is a conscious choice rather than a mechanical failure. This, he says, is why factors that alter a person’s perception or motivation (monetary rewards, for example) can affect performance, even without any change in muscle capacity. In the subliminal experiments, the cyclists’ heart rates and lactate levels rose at the same rate no matter which faces they saw, indicating that nothing had changed from the neck down. Considerations like heat, hydration, and muscle conditioning, Marcora says, “are not unreal things, but their effect is mediated by perception of effort.” In other words, they don’t force you to slow down, as happens with the failing frog muscles in the petri dish; they cause you to want to slow down—a semantic difference, perhaps, but a significant one when it comes to testing the outer margins of human capability.

Read more: “What Is Fatigue?” – The New Yorker

Also published on Medium.