The human brain works harder when playing sport against robots.
Experts from the University of Florida have analysed hours of table tennis matches where humans were pitted against both man and machine.
Players were fitted with electrode caps to monitor their brain activity during the games and found that the nerve cells in their brains were aligned differently when facing a ball-serving machine in a phenomenon known as desynchronisation.
Daniel Ferris, a professor of biomedical engineering at the University of Florida, said: "If we have 100,000 people in a football stadium and they're all cheering together, that's like synchronisation in the brain, which is a sign that the brain is relaxed.
"If we have those same 100,000 people but they're all talking to their friends, they're busy but they're not in sync.
"In a lot of cases, that desynchronisation is an indication that the brain is doing a lot of calculations as opposed to sitting and idling."