While it's long been understood the abilities of our brains separate human beings from all other life on Earth, a new study suggests human muscles themselves are pretty special as well.

Scientists in China examined the evolution of metabolites -- small molecules like sugars, vitamins and amino acids -- that play key roles in the human body's physiological functions, explained a research group news release.

The study, published in the open-access journal PLOS Biology, revealed metabolite concentrations evolved rapidly over the course of human evolution in two types of tissues, in the brain and muscles.

The human genome, explained the study, changes steadily through time, yet only a few of those changes were likely responsible for the development of distinct human features.

To identify what other factors outside the genome affected human evolution, researchers from the Shanghai-based Chinese Academy of Science-Max Planck Gesellschaft Partner Institute for Computational Biology, took the first official scientific look ever at the human metabolome, the collection of metabolites present in human tissues.

"Metabolites are more dynamic than the genome and they can give us more information about what makes us human," research leader Philipp Khaitovich said in the 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."

Unlike the human genome's generally uniform pace of evolution, it was discovered the metabolome of the human brain has evolved four times faster than that of the chimpanzee, and that human muscles demonstrated an even higher amount of metabolic change -- 10 times that of the chimpanzee.

"For a long time we were confused by metabolic changes in human muscle," said Kasia Bozek, the lead author of the study, "until we realized that what other primates have in common, in contrast to humans, is their enormous muscle strength... 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."

To test their assumptions, researchers staged a pulling strength competition between several chimpanzees, macaques, university students and professional athletes. Despite their great effort and determination, all of the human participants of the experiment were outperformed by their primate opponents 2 to 1.

Joseph Call from the Wolfgang Kohler Primate Research Center in Leipzig, Germany said the insights gained from the latest research have been "common knowledge to all the zoo keepers, but it was never tested systematically."

Said Bozek:"The world of human metabolomics is just starting to open up its secrets to us."