In an increasingly busy world, listening to a podcast, watching a documentary or even learning a foreign language while exercising may feel like a constructive use of time.
But a new study suggests that when the body is forced to carry out mental activity at the same time as physical exertion, the brain will win, and performance is likely to suffer.
Scientists at the University of Cambridge were curious to calculate the trade-off between physical and mental capacity when the body and brain are both forced to work hard.
They asked elite rowers from the Cambridge University Boat Club to take part in a mental recall test while exercising strenuously on a rowing machine.
Although all the athletes suffered both a drop in both mental and physical performance, it was their ability to row which was the most harmed.
The findings suggest that for athletes who are keen to improve their performance, quieting the mind and switching off from mental distractions, such as podcasts, could help.
Dr Longman, of Cambridge’s Department of Archaeology, said: “Mind state and thought processes can influence physical performance. Focusing on the activity itself, rather than letting the mind wander, can enhance performance in high level and high intensity sporting disciplines.
“From a personal perspective, I recently found on an Arctic expedition that clearing the mind completely allows endurance performance that far exceeds anything you might previously imagine you're capable of. I have heard the same thing from other ultra-endurance athletes.
“There is evidence suggesting that the ability to 'dissociate' from a physical task, i.e. think about something else, like a podcast enhances performance in recreational athletes by distracting them from the discomfort of the activity itself.
“In high-level elite athletes, the story would likely be different, and a podcast might well reduce performance.”
Researchers believe that humans have evolved to prioritise quick thinking over fast movement, which helped our ancestors to survive.
Metabolically speaking, human brains are expensive, requiring a lot of energy to run. The new study suggests that when forced to choose between fuelling the brain or the muscles, the body picks the brain, sending more glucose to neurons at the expense of other areas , a trait dubbed the ‘selfish brain hypothesis.’
The ‘selfish’ nature of the brain is most evident in people who have faced long-term starvation or malnutrition, where their bodies have wasted away yet their brain matter is still intact.
For the new study, Cambridge's PAVE (Phenotypic Adaptability, Variation and Evolution) research group tested 62 male students with an average age of 21.
The rowers performed two separate tasks: one memory, a three minute word recall test, and one physical, a three minute power test on a rowing machine.
They then performed both tasks at once, with individual scores compared to those from previous tests.
During the simultaneous challenge, recall fell by an average of 9.7 per cent, while power fell by an average of 12.6 per cent. Across all participants the drop in physical power was on average 29.8 per cent greater than drop in cognitive function.
Dr Longman, said a well-fuelled brain offered early humans better survival odds than well-fuelled muscles when facing the challenges that come from living in complex societies.
“In our evolutionary past, humans are believed to have transitioned from a ‘soldier’ to a ‘diplomat’ lifestyle,” he said.
“We began to invest fewer resources in developing and maintaining high levels of muscularity, and instead began to achieve status through the development of enhanced social manipulation skills.
“Today's society is highly integrated, and during a typical day we are required to process quantities of information that are unparalleled throughout history. Prioritising cognitive function is most definitely helpful in the world we have created.”
The research was published in the journal