The difference in size is not much, an adult male can reach 1.7m but the length of the arm bones is impressive, which means a great lever and a lot of muscle, in addition to the fact that they spend their time jumping from tree to tree and they can be held, hung and brought back up all over the body with just the strength of your arms.
If we look closely, we must have respect for them:
The thickness of the musculature of the arms can be equivalent to the thighs of a human, remember that they walk supported on their arms.
Unlike humans, they have almost no body fat, all muscle and denser
An adult can weigh 60 to 80kg, the same as a human.
Another important factor is the type of muscle fiber, due to the length of the arms and the use they give them, chimpanzees evolved to develop much more long muscle fiber, which favors strength over the precision that the short muscle fiber gives. They have the MYH16 gene active that favors long fiber, this gene is inactive in humans (with very few exceptions)
As you can see in the photo I uploaded, the length of the arm and forearm makes the muscle that connects and pivots both bones very long as well, which together with the exercise they do (walking on their arms and climbing trees) favors training of longer muscles, with a larger cross-section and with a larger long muscle fiber.
One of the muscles that connects the forearm with the arm projects beyond the middle of the arm, approaching the wrist, which together with the biceps and triceps, provides a great lever that they use to be able to climb with great ease and hit:
This muscle called the Brachioradialis, which we humans also have, runs through the entire arm from the forearm to the hand and since it is longer in chimpanzees they have the opportunity to develop it more and with long fibers, together with the use they give to the arms both for walking and climbing.
It should be clarified that it is false that they are 3 or 5 times stronger, this was based on wrong conclusions published at the beginning of the last century. They are actually 1.25 to 1.35 times stronger than a very strong man, maybe 1.5, obviously more depending on who you compare him to.
But a chimpanzee will not hit you by throwing a straight punch, rather he will raise his arms and unload with the force of his whole body that together with the length of his arms will produce a greater lever making a hammer effect, the same movement that he uses instinctively to break a cocó or a shell of some prey that has been hunted.
As the experts at the Lester Fisher Center explain:
” In chimps, the muscle fibers closest to the bones — those deemed to be the source of strength of both chimps and humans – are much longer and denser, so a chimp is able to generate more power using the same range of motion, Ross of the Lester Fisher Center .”
” In chimpanzees, the muscle fibers closest to the bones, which are considered the source of strength in both chimpanzees and humans, are much longer and denser, so they can generate more energy with the same range of movement.
Lester Fisher Center “
As can be seen, they have much less body fat than the average human, long muscle fiber density is higher than in humans.
Most chimpanzees do not require fat for thermal protection: