A new study finds that exercise not only
causes muscle fatigue but could also
affect the brain. The authors conclude
that overexercising might reduce our
capacity to make decisions.

A recent study concludes that intensive exercise
may affect cognitive abilities.

Researchers at Hôpital de la Pitié-Salpêtrière in
Paris, France, have found that overtraining syndrome
may affect the brain, as well as the rest of the
body.

Overtraining syndrome is a form of burnout in
endurance athletes. It occurs as a result of intensive
physical training overload.

The authors believe that this form of fatigue may
involve some of the same neural circuitry as the
fatigue that follows intensive intellectual work.

Scientists have already found that fatigue following
excessive mental effort can affect cognitive control.

Cognitive control, sometimes called executive
control, refers to a person's ability to change their
behavior and thought processes to achieve their
goals.

Inducing overload
A physical training overload leads to a significant
drop in physical performance as athletes experience
an overwhelming sense of fatigue.
 The researchers
wanted to test whether overtraining syndrome arises
in part from neural fatigue in the brain, as well as
from muscle tiredness.

They were also interested in whether the overtraining
affected the same portion of the brain as excessive
intellectual work.
The group recruited 37 competitive male endurance
athletes with an average age of 35 years. The
participants either continued with their regular
exercise regimen or increased their training by 40%
per session over 3 weeks.

The athletes participated in cycling exercises on
their rest days so that the researchers could
monitor their physical performance.
 They also
completed questionnaires that asked them about
their subjective experience of fatigue.

Finally, the researchers used behavioral tests and
MRI scans to assess the participants' cognitive
ability.

Assessing the effect
The study, which features in Current Biology , showed
that over 3 weeks, physical training overload led to
the athletes feeling more fatigued and also
behaving differently.

In tests that evaluated economic choices, the
fatigued athletes were more likely to act
impulsively.

MRI scans showed that physically overloading the
athletes resulted in impaired activation of the lateral
prefrontal cortex. This area of the brain is
responsible for higher order cognitive control;
 it
influences decision-making, planning, behavioral
inhibition, and motivational operations, among other
behaviors.