It’s important to see our evolutionary traits as features sometimes, instead of bugs. Evolution has turned out plenty of bugs, but unpleasant responses like confusion, boredom and fatigue are definitely features.
BIO: Muscles and brains need physical energy, supplied by oxygen and glucose, which are used to make the ATP that energizes muscle contractions or action potentials. When the body is deprived of these resources, muscle fatigue results and our clarity of thinking may also be affected. However, mental fatigue often occurs without an exhaustion of resources. The problem we often run into is that physical fatigue and mental fatigue feel about the same!
I think most of us rarely stop to wonder which kind of fatigue we’re experiencing. We just complain about brain fog; but self-reported fatigue, from many causes, often has genetic roots. We experience physical and mental relief from some drugs, like modafinil.
PSYCHO: Physical fatigue is certainly real, and so is a mental component that has been largely neglected until recently. Fatigue apparently is separate from exhaustion. It’s a body governor that we can override, though not without consequences. Or exaggerate, though not without consequences.
There are many causes of fatigue, some pretty exotic or obscure, and although mental fatigue seems to be a regulator of effort there does not seem to be a regulator of fatigue. It’s involuntary, though just as with hunger, we can sometimes push past it. We cannot push past physical collapse when muscle resources have been exhausted.
Muscular fatigue is real, but it’s not all there is to fatigue. Mental fatigue, a combination of cognitive overload and stress, is just as real. Mental fatigue degrades muscular performance, and muscular fatigue impairs learning.
A lot of people get tired just because they want to be always productive. Interestingly, the road to higher productivity has rest stops. Without downtime, working (and workouts) can feel like constant fatigue.
It’s hard to deny the cost of mental effort. The problem, though, is that fatigue is impossible to prevent* because it’s hard to explain, even if we ignore disease as a factor. You might take a look at the attached article, below. It’s easy to suspect that getting tired from exercise is what fogs the brain, but sometimes it’s the reverse—mind over body when both get tired.
SOCIAL: There are social forms of fatigue, such as compassion fatigue and the hydra-headed fatigue monster that sometimes invades teaching. But students commonly suffer sleep deprivation in high school and college that impairs attention and memory.