Muscle fatigue is largely a psychological illusion created by your nervous system to prevent you from physically destroying your own tendons and fibers.

A closer look

Muscle fatigue is largely a psychological illusion created by your nervous system to prevent you from physically destroying your own tendons and fibers. When you feel completely exhausted during a workout and think you cannot possibly do another rep, your muscles still have plenty of energy reserves, but your central governor steps in and shuts down the signal. Your brain basically treats you like a reckless toddler driving a sports car, forcibly cutting the engine before you can do any permanent structural damage. This means you are physically much stronger than you think, but your overprotective nervous system refuses to let you access your full potential just in case you need to outrun a bear later