Animals

The Super Strength of Chimpanzees, Explained

A study shows that chimps have more “fast-twitch” muscle fibers that enable sudden strength, while humans have more of the “slow-twitch” fibers that enhance endurance.

Since then, numerous other experiments have attempted to measure the strength of chimpanzees versus that of humans, with most concluding that chimpanzees are “super strong” compared to our species. New research, published in the journal Proceedings of the National Academy of Sciences, confirms the long-standing theory, finding that chimps and humans differ in mass-specific muscle performance by 1.5 times. This means that, pound for pound, chimps are indeed much stronger than humans.

“Humans can’t exercise their way to chimpanzee-like muscle,” lead author Matthew O’Neill of the University of Arizona College of Medicine-Phoenix said. “But the experimental data show that we can certainly add muscle mass and outperform smaller chimpanzees in terms of absolute weight moved.”

O’Neill and his colleagues began their investigations with a review of all existing experimental data on chimp strength, including Bauman’s 1920s studies. The scientists then directly measured the properties of muscle fibers sampled from three young male chimpanzees and compared these measurements with those for human muscle fibers. The researchers additionally conducted biomechanical assessments of muscle proteins.

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The analysis found that the inherent contractile properties of human and chimp skeletal muscle fibers — maximum force and shortening velocity — are similar. The length and composition of the fibers, however, differ between chimps and humans. Chimps have more of what are known as “fast-twitch” fibers that permit tremendous sudden strength, such as what is needed to suddenly pull something, to jump, and to make a quick getaway.

Humans, conversely, have more “slow-twitch” fibers that enhance endurance, such as allowing for long walks or jogs. Ideally, an individual would exhibit both impressive inherent strength and endurance, but that is not technically possible.

“It’s a zero-sum game, at least in terms of percentages,” O’Neill explained. “Increasing slow fibers means decreasing fast ones, and vice versa.”

The study reveals more about humans than chimps, since most primates exhibit similar muscle properties. This suggests that the common ancestor of humans and other primates had muscles that were more chimp-like. Humans are therefore “the outliers,” as O’Neill said.

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“We know from the fossil record that there are shifts towards more over-ground locomotion in the hominin lineage about 4 million years ago, and (there was) the emergence of hunting and gathering about 2 million years ago,” he added, indicating that these changes might have promoted, or been evidence of, muscles better suited for endurance activities.

Slow-twitch muscle fibers confer other benefits. He said they allow for efficient diffusion of oxygen into the blood stream. They can also be turned on and off more without fatiguing.

“So, from the standpoint of muscle metabolism, these are traits that are beneficial for behaviors requiring low cost, repetitive (muscle) contractions, like long-distance walking and running,” O’Neill explained.

Humans can out-muscle certain chimps in activities like weight-lifting, so long as the person has gone through a lot of training and added substantial extra muscle mass. A well-designed exercise regime can also impact an individual’s muscle fiber type, but the person would never be able to match the muscle structure of chimps, since these primates have twice as many fast-twitch muscle fibers as slow-twitch ones.