A chimpanzee is roughly 1.35 to 1.5 times stronger than a human of similar size. That’s the finding from the most rigorous modern research, published in the Proceedings of the National Academy of Sciences in 2017. It’s impressive, but far less than the old claims of chimps being five or even ten times stronger than people, figures that circulated for decades based on flawed early experiments.
Where the “Super Strength” Myth Came From
Reports of extraordinary chimpanzee strength date back to the 1920s. In one widely cited set of experiments, chimps motivated by rage or curiosity pulled a handle attached to a dynamometer, producing forces three to four times greater than men of equivalent body weight. But these tests had serious problems. The chimps were highly aroused and pulling with everything they had, while the human comparison subjects were calm volunteers. A later experiment using eight adult chimps pulling a rope (without a handle) for food rewards found their performance was only slightly better than humans, pound for pound.
Those early, sensational numbers stuck in the popular imagination. The more careful modern estimate of 1.5 times greater performance, based on a broad review of available data, and the 1.35 times figure from computer simulations of whole-muscle mechanics, tell a more grounded story. Chimps are genuinely stronger than us relative to body mass, but not by the wild margins people assume.
Why Chimp Muscles Produce More Force
The key difference is muscle fiber composition. About 67% of chimpanzee muscle is made up of fast-twitch fibers, the type that generate rapid, powerful contractions. Humans have the opposite ratio: our muscles are dominated by slow-twitch fibers, which make up roughly 53 to 69% of our limb and trunk muscles depending on the study. Slow-twitch fibers are built for endurance and sustained, controlled effort. Fast-twitch fibers are built for explosive bursts of force.
This fiber composition alone accounts for much of the strength gap. When researchers built computer models simulating chimpanzee and human muscles of the same size, the chimp muscle’s higher proportion of fast-twitch fibers produced 1.35 times more dynamic force and power output. In other words, even if you gave a human and a chimp identical amounts of muscle tissue, the chimp’s muscle would still outperform because of what it’s made of.
The Nervous System Factor
Muscle fibers are only part of the explanation. Evolutionary biologist Alan Walker at Penn State University has argued that our nervous systems play an equally important role. Compared to chimps, humans have significantly more grey matter in their spinal cords relative to body mass. That grey matter contains motor neurons, the nerve cells that connect to muscle fibers and control movement.
More motor neurons means each one controls a smaller bundle of muscle fibers. This gives humans fine-grained control: you can thread a needle, play piano, or write with a pen because your brain can recruit tiny, precise portions of a muscle. Chimps have fewer motor neurons, so each one fires a larger group of fibers. Using a muscle becomes closer to an all-or-nothing event. A chimp reaching for a fruit often recruits more muscle than the task actually requires, which makes the movement more powerful but less precise.
There’s also likely a layer of neural inhibition in humans that prevents us from routinely pushing our muscles to their structural limits. This protects our tendons, ligaments, and bones from damage. Chimps appear to lack this safeguard to the same degree, meaning they can access more of their available muscle power in everyday movements.
Explosive Power in Action
The practical difference shows up dramatically in tasks that demand explosive output. Researchers studying bonobos (close relatives of chimpanzees with similar physiology) measured their vertical jump height. All three bonobos tested cleared 0.7 meters or more during the airborne phase. A typical human maximal jump reaches only 0.3 to 0.4 meters.
What’s striking is that the raw mechanical output was nearly identical. A 34-kilogram male bonobo and a 61.5-kilogram human male both produced about 450 joules of energy and roughly 3,000 watts of peak power during push-off. The bonobo achieved nearly twice the jump height with almost half the body weight. The difference came down to how efficiently the bonobo’s muscles, particularly those around the hips, converted that energy into movement. The hip muscles alone delivered mass-specific power output of 615 watts per kilogram, a figure that reflects the explosive potential of fast-twitch-dominant muscle.
Anatomy Works Differently Too
Beyond muscle composition and neural wiring, the physical structure of chimpanzee limbs is built for a different set of tasks. Chimps have shorter lever arms at the ankle compared to humans. When researchers scaled moment arm lengths by foot size, chimpanzee values were consistently smaller across nearly every muscle measured. Shorter lever arms sacrifice mechanical advantage for speed and range of motion, which suits climbing and swinging through trees.
Chimpanzee ankles also have far greater range of motion. Their total ankle flexion averages about 98 degrees, compared to 60 to 71 degrees in humans. Their foot inversion and eversion range hits 68 degrees, roughly double the human range of 29 to 41 degrees. This extra mobility makes chimps remarkably versatile climbers but comes at the cost of the stability humans need for efficient upright walking and running.
What Humans Gained by Getting “Weaker”
The shift toward slow-twitch muscle fibers in human evolution wasn’t a loss. It was a trade. Slow-twitch fibers fatigue much more slowly, which made humans exceptional endurance athletes. Early humans likely used persistence hunting, chasing prey over long distances until the animal overheated, a strategy that depends entirely on sustained, moderate muscular effort.
The increase in motor neurons and fine motor control opened up toolmaking, precise throwing, and eventually every manual skill that defines human culture. A chimpanzee can crack a nut with a rock, but it can’t knap a stone tool to a fine edge or throw a spear with accuracy. Those abilities required the nervous system changes that cost us raw power. The trade-off shaped nearly everything about how humans interact with the world: we build and manipulate rather than overpower.