RACHEL MARTIN, HOST:
Athletes who train too much don't just exhaust their bodies, they exhaust their brains. That's according to a new study from researchers in France. And it may explain why elite athletes sometimes see their performance decline as they ramp up training. Here's NPR's Jon Hamilton.
JON HAMILTON, BYLINE: The world's best distance runner in the early 1980s was Alberto Salazar.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED PERSON: Salazar kicking - go, go.
UNIDENTIFIED PERSON: Pushing off the final challenge by Beardsley for the win, the 1982 Boston Marathon.
HAMILTON: He won the Boston Marathon once and the New York City Marathon three times. Then Salazar stopped winning, even though he was still in his mid-20s and training harder than ever. Bastien Blain, a researcher at University College London, thinks he might know why.
BASTIEN BLAIN: Probably there was something linked to his brain and his cognitive capacities.
HAMILTON: Blain's hunch comes from a study of 37 male triathletes who took part in a special training program.
BLAIN: They were strongly motivated to be part of this program, at least at the beginning.
HAMILTON: Half the triathletes were told to continue their usual workouts. The other half were told to train a lot harder. The training was so intense, the athletes began to perform worse on a cycling test. Blaine says, after a few weeks, all the participants were put into a brain scanner and asked a series of questions.
BLAIN: For example, we asked, do you prefer $10 now or $50 in six months?
HAMILTON: The answers showed a clear difference in the over-trained athletes.
BLAIN: Those people were, in fact, choosing more immediate gratification than the other group of athletes.
HAMILTON: And Blain's team reported in the journal Current Biology that the athletes also had less activity in one part of the brain.
BLAIN: It was a very little brain area, a little spot of the left prefrontal cortex that's impacted during decision making.
HAMILTON: Lots of activity in that area seems to help an athlete decide to keep pushing. But when an athlete trains too hard, Blain says, the activity level stays low and their performance suffers.
Tanja Mueller is part of a research team at the University of Oxford that was not involved in the study. Mueller says her team also sees a link between physical exertion and decision making.
TANJA MUELLER: We find that people, as they have repeatedly exerted effort over time, they tend to be less willing to keep exerting effort for rewards, in particular high efforts.
HAMILTON: But Mueller isn't so sure the brain is simply choosing immediate gratification. She says when the body gets really tired, the brain can experience something called motivational fatigue.
MUELLER: People may not consider it worth it anymore to wait for higher rewards to be received.
HAMILTON: So they don't try as hard. Mueller says activity in the brain's left prefrontal cortex does seem to play a role in fatigue and decision making. But she says two other areas also seem to be important.
Another scientist who studies motivation is Todd Braver of Washington University in St. Louis. He says when an athlete pushes their body in a race, the brain is also working hard to answer lots of questions.
TODD BRAVER: How close am I to this goal? What is my physiological depletion versus, you know, the expected benefit I'm going to get for reaching the end of the race? Should I make a decision that it's time to quit?
HAMILTON: Braver says, to the brain, this last question is all about costs versus benefits. And as fatigue increases, he says, so do the costs until they get too high.
BRAVER: The brain might kind of have this built-in mechanism to say, hey, it's time to, you know, shift from this goal to another one.
HAMILTON: Like getting some rest. Jon Hamilton, NPR News.
NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.