In a previous post I discussed the idea that fatigue, much like pain, is a subjective experience created by the brain to protect you from physical threats caused by the stress of heavy physical exertion. So when we experience fatigue, it's not so much that the body can't, it's that the brain won't. An interesting study just came out that adds an interesting wrinkle to this perspective.
Researchers asked participants to do arithmetic while doing reps of shoulder raises. Guess what, you are weaker when you are doing math in your head. The researchers speculated that the brain power devoted to doing math diverted mental energy from the concentration and focus necessary to continue activating the motor neurons that were being inhibited by the fatigue. Maybe this explains the common stereotypes about math geeks and muscle heads. One thing is for sure - I will stop doing sudoku puzzles while leg pressing.
This also reminds me of the concept called "ego depletion" which I am currently reading about in a book called Willpower. The basic idea is that willpower is a limited resource, and if you use it for some challenging activity such as doing an unsolvable puzzle or trying not to laugh at a funny movie, you will have less left over for resisting the urge to eat tasty treats or yell at an annoying jerk (these are actual experiments!)
More fascinating evidence that physical performance is a complicated interplay between the state of the body, the brain's evaluation of threats caused by exercise, and the brain's ability to focus resources and attention on the task at hand.
Hat tip to Alex Hutchinson at Sweat Science for news on the study.