Looks like I really am a softy, after all Joel Sartore, National Geographic Photo Ark

Chimpanzees do have stronger muscles than us – but they are not nearly as powerful as many people think.

“There’s this idea out there that chimpanzees are superhuman strong,” says Matthew O’Neill at the University of Arizona in Phoenix. Yet his team’s experiments and computer models show that a chimpanzee muscle is only about a third stronger than a human one of the same size.

This result matches well with the few tests that have been done, which suggest that when it comes to pulling and jumping, chimps are about 1.5 times as strong as humans relative to their body mass. But because they are lighter than the average person, humans can actually outperform them in absolute terms, say O’Neill.


His findings suggest that other apes have similar muscle strength to chimpanzees. “Humans are the odd ones,” he says.

O’Neill’s team has been studying the evolution of upright walking. To create an accurate computer model of how chimps walk, the researchers needed to find out whether their muscles really are exceptionally strong. So they removed small samples of leg muscle from three chimps under general anaesthetic and measured the strength of individual fibres.

The same procedure is used to study human muscles. Comparing the results with the many studies on those revealed that, contrary to the claims of several other studies, there is nothing special about chimp muscle. “Chimpanzee muscle is really no different than human muscle in terms of the force that individual fibres exert,” says O’Neill.

Fast twitchers

So why, on a pound-for-pound basis, are chimps slightly stronger than humans? The team went on to look at the muscle of chimps that had died of natural causes, which revealed that two-thirds of their muscle consists of fast-twitch fibres, whereas more than half of human fibres are slow-twitch. Fast-twitch fibres are more powerful, but use more energy and become fatigued faster.

Another factor, O’Neill found, is that chimps have longer fibres on average, which also enhances their strength.

This adds to the evidence that walking is considerably more energy-costly for chimps than for people. The results fit neatly with the idea that early humans evolved to walk or run long distances. It seems that we sacrificed some strength for greater endurance.

An earlier study found that our jaw muscles are particularly weak, which may have helped our brains grow larger.

Quite how the myth that chimps are incredibly strong came about is not clear, says O’Neill. But it may have been fuelled by a 1923 study that claimed one chimp could pull nine times its own body weight. Later studies suggested they could only pull two to four times their weight.

Journal reference: PNAS, DOI: 10.1073/pnas.1619071114