Basically what the title says. If exhaustion resulting from physical activity is caused because our body struggles to keep up with the metabolic energy demand of our body but pretty much every source says that our brains energy consumption does not vary significantly with the amount of mental effort that we are doing then what exactly causes mental fatigue and exhaustion.
Eli5: If you are a healthy, able-bodied person, balancing is not usually an issue. You stand and walk with only minimal exhaustion. You can also run for a decent amount of time without getting too exhausted.
All of these tasks are so different, yet equally complex. Merely standing requires you fighting gravity. Walking requires this, plus added energy and coordination. Running requires all that, plus endurance and even more expended energy.
The average human’s brain function is probably similar to standing. You are actively parsing your surroundings for stimuli, but allowing yourself to daydream, plan ahead, etc.
When you actively try to focus on something, especially any sort of complex task that involves problem solving or adapting, that is more akin to running. In high stress environments, doing this same action is akin to sprinting. Unless you’re trained to endure it, your brain will fatigue quite easily when doing this.
Your brain is a muscle, but more like a series of muscles like your ‘core’. The harder you push it, the more it will tire, until it hits a ceiling, or raises it. Your body requires the same amount of energy to do complex tasks rapidly in high stress environments as it would to sprint for a very long distance.
I can’t get into the reasoning behind it not having as immediate if a physical effect (I.E.: weight loss, muscle growth)— this is beyond my level of knowledge and is slightly above ELI5
Not exactly ELI5, but analogies can be helpful
The brain is a very complex organ that controls all the functions in our body, including our thoughts, feelings, and behaviors. When we engage in mental tasks that require attention, focus, and problem-solving, different areas of the brain are activated and work together to process and integrate information.
This neural activity requires a lot of energy and resources, such as glucose and oxygen, to maintain optimal function. In fact, the brain consumes about 20% of the body’s energy, despite only accounting for about 2% of its weight!
When we engage in sustained mental effort, we use up these energy and resource reserves, leading to a state of mental fatigue or exhaustion. This can manifest as decreased motivation, difficulty concentrating, slower reaction times, and decreased accuracy on tasks.
Interestingly, research has shown that mental fatigue can have a greater impact on our performance than physical fatigue. This is because physical fatigue typically affects only the muscles, whereas mental fatigue affects the brain, which is responsible for coordinating and controlling all the body’s movements and responses.
In summary, mental effort exhausts us because it requires a lot of energy and resources from our brain, leading to a state of mental fatigue that can impact our performance and well-being.