It is often amusing to see chimpanzees in a zoo. But the idea of going inside the cage to shake hand with one is not always delightful to many.
Both wild chimpanzees and those under confinement are known as super-strong primates since 1920s. Previous reports and controlled experiments have suggested that the strength of our closest living relatives, chimpanzees, is higher than us, modern humans, by many folds.
However, a review of literature done recently on studies conducted between 1923 and 2014 suggests that chimpanzee’s mass-specific muscular performance is only 1.5 times higher than humans on an average.
Perhaps digging into such a vast pool of literature to collect data was difficult and maybe misleading. Moreover, most of the studies have used experiments, such as pulling weight, to evaluate the strength between humans and chimpanzees. These studies link muscle mechanics to whole body performance. This makes it difficult to estimate exact muscular strength from these kinds of experiments.
Higher body mass, higher amount of muscle-tendon units, and larger moment arms may facilitate chimpanzees perform better in this type of pulling exercises than humans.
“There are nearly 100 years of accounts suggesting that chimpanzees must have intrinsically superior muscle fiber properties compared to humans, yet there had been no direct tests of that idea,” says Brian Umberger from the University of Massachusetts Amherst.
THE SCIENCE BEHIND IT
Many hypotheses were proposed to evaluate differences in muscular activity between chimpanzees and humans. However, the prominent ones include higher isometric tension-producing capacities, faster maximum shortening velocities. Differences in myosin heavy chain distribution in the skeletal muscle is also considered by some as important.
Static strength or isometric tension-producing capacity of a muscle is its ability to generate tension without changing its length. In contrast, maximum shortening velocity is the maximum rate of muscle shortening.
To conduct this experiment, researchers isolated muscle fibers. The strength and velocity of muscle contraction, as well as distribution of a specific muscle protein, called myosin, was studied further.
Results reveal that the secret behind chimpanzee’s strength is due to higher content of fast-twitch muscle fibre in the skeletal muscle.
There are basically two kinds of muscle fibres, fast-twitch and slow-twitch. Fast-twitch fibres generate higher amount of force but fatigue easily – a condition associated with sprinters. In contrast, slow-twitch fibres generate less force but can sustain it for a longer time – like endurance activities.
Both fast and slow-twitch fibres also maintain specific myosin heavy chain isoform patterns.
To add more into muscle architecture, researchers found that chimps have longer muscle fibre length and higher content of myosin heavy chain type II isoform. This in turn attributes to higher dynamic force and power-generating capacities in chimpanzee as compared to human.
“We found that within fibre types, chimp and human muscle fibres were actually very similar. However, we also found that chimps have about twice as many fast-twitch fibres as humans,” says Umberger.
Moreover, researchers have used their data into a computer simulation, which suggested a chimpanzee-human muscular performance difference of about 1.35 times – a value which is almost equal to the one they have estimated based on pieces of literature.
Taken together, researchers have concluded that in contrast to many previous hypotheses, evolution did not change the force, velocity, or power-generating capacities to increase muscular performance in chimpanzees compared with humans.
Alternatively, natural selection appears to play important role in altering the structural architecture of muscle. Maybe length and distribution of muscle fibres might be an attribute of natural selection.
“When we compared chimps and humans to muscle fibre type data for other species we found that humans are the outlier, suggesting that selection for long distance, over-ground travel may have been important early in the evolution of our musculoskeletal system,” says Umberger.
Scientifically speaking, you can challenge a chimp next time, but not that we suggest. Read more here.