A new study suggests that humans traded muscle power for better brains.

The study, conducted by researchers at Shanghai's CAS-MPG Partner Institute for Computational Biology, found that accumulation of metabolites - small molecules of sugar, vitamins, amino acids and neurotransmitters - was faster in both, brains and muscles, over the course of human evolution.

Metabolites are small molecules produced during metabolism. These molecules are important during DNA and protein synthesis.

Researchers say humans switched energy-consumption between muscles and brains, which helped them in acquiring better cognitive abilities. Chimps and other primates, on the other hand, developed strong muscles, but a weak brain.

The study is unique because it moved away from genomic research and looked into the role of other molecules.

Dr Philipp Khaitovich from Shanghai and team examined the evolution of the human metabolome. The research was based on analysis of 10,000 metabolic molecules, National Geographic reported.

For the study, researchers examined metabolite levels in kidney, muscles and brain, Livescience reported.

"Metabolites are more dynamic than the genome and they can give us more information about what makes us human," said Khaitovich in a news release. "It is also commonly known that the human brain consumes way more energy than the brains of other species; we were curious to see which metabolic processes this involves."

The team found that genome has evolved at a steady pace, whereas metabolome of the human brain evolved four times faster than in the chimpanzees. Human brain started using lots of energy to evolve into a super-processing machine, which helped humans control nature.

On the other hand, metabolism rate in primates remained almost unchanged - which meant that they had better muscle power but poor cognitive skills.

The research team conducted several tests including chimpanzees, macaques, university students and even professionals. They found that other primates had two times better muscle strength than human competitors.

Researchers hypothesize that weak muscles was the price that humans paid to get better brains.

"Our results suggest a special energy management in humans, that allows us to spare energy for our extraordinary cognitive powers at a cost of weak muscle," summarized Dr Kasia Bozek, the lead author of the study. 

The study is published in the journal PLOS Biology