Brains beat brawn in your body’s battle for metabolic resources
When running a race, lifting weights or swimming laps, the last thing you should be thinking about is math problems. Or special relativity. Or how to simplify the tax code, when you last called your mother or any other topic that might require more than minimal brain power. It’s not that these topics might take you out of “the zone” and break your rhythm, but that these thoughts all require energy to process. That energy is limited, and researchers have found that your brain will take its share first, which may leave your muscles working off your metabolic leftovers.
We’ve long known that the brain is an energetically expensive piece of anatomy. On a daily basis, our brains are estimated to demand up to 20 percent of our resting metabolic capacity even though they’re usually only two percent of our body weight. As a species we’ve prioritized our brains so much that babies’ heads barely fit through their mother’s birth canal, making childbirth a potentially dangerous endeavor. With this in mind, researchers wanted to see if we also favored our gray matter on a smaller time-scale, testing how athletes handled mental activity while simultaneously working their muscles.
Rowing while remembering
The study asked 62 rowers to do two basic tasks. First they rowed vigorously for three minutes. Then they did a short word-recall task that really only tested their memories. No real calculations or insight was needed. With these baselines for comparison, researchers asked participants to do both tasks at once. As you’d expect, the combined activities were harder than doing one at a time, but not to the same degree. While rowing made recalling words harder, those scores didn’t drop off as much as the rowing itself. When in direct competition for metabolic resources, it seem that muscles got the short end of the stick, as physical performance suffered 29 percent more than mental performance.
The metabolic tug-of-war in question is over oxygen and glucose. Skeletal muscles need a lot of those resources as well, but when both are in demand at once brains seem to get first dibs. As with the other adaptations our species has made to power our brains, it’s thought that a sharp mind must have made our ancestors more successful than fully-fueled muscles did. The average athlete probably isn’t worried about starving their muscles for the sake of their brain’s glucose supply, but avoiding this metabolic battle may be another reason to try to keep a clear head when you’re working out.
Source: ‘Selfish Brain’ Wins Out When Competing With Muscle Power, Study Finds by Danny Longman, Scienmag
