Paul Anderson may have been the strongest man that ever lived. He could carry eight people on his back, or drive a nail through two planks of wood with one blow.
In 1957, Anderson apparently lifted 6,270 pounds (2.8 tonnes) on his back. This temporarily earned him a world record, but the record was subsequently taken away due to a lack of supporting evidence.
While some have come close, nobody has ever topped Anderson's feat. At least, no human has. But elsewhere in the animal kingdom there are creatures capable of truly prodigious feats of strength.
Staying with the back lift, humans have a long history of loading up animals as beasts of burden. In the west, packhorses have been used since the Stone Age to carry heavy loads across uneven ground.
James Watt developed the concept of horsepower based on an experiment involving horses working a mill stone at a brewery
While a 2008 study suggested that light horses should carry no more than 20% of their bodyweight, their heavy counterparts were specially bred for strength.
By selectively breeding the biggest animals, people created giants like Shire horses and Clydesdales. These heavy horses are known as "draught horses" because of their pulling power. They effectively dragged us through the Industrial Revolution, first pulling carts and coaches, then barges and wagons of material for the railways.
In fact, when steam engines came along they were compared to the prodigious pulling power of horses.
Scottish engineer James Watt developed the concept of horsepower based on an experiment involving horses working a mill stone at a brewery. He calculated that one horse could lift 33,000lbs (15 tonnes) one foot into the air in one minute.
Working Shires can comfortably pull twice their weight
This is sometimes regarded as an over-estimate of the average heavy horse's strength, although a 1993 study entitled simply "Horsepower from a horse" concluded that Watt got it about right. Regardless, the measurement stuck and is still used to describe engine power today.
Draught horses are still employed by a few traditional breweries for pulling carts, and are popular tourist attractions. They have also been embraced for forestry management, since they cause less disturbance to the environment than heavy machinery.
"Shires have the same musculoskeletal structure as any other horses," says Angela Whiteway of the Shire Horse Society in Market Harborough, UK. "However, it is thought that having the hind legs set close together enables them to engage their power more effectively than if the hind legs are set wide apart."
Whiteway says it is generally accepted that working Shires can comfortably pull twice their weight, meaning an average 1-tonne horse can pull 2 tonnes in weight. That is impressive, but other animals can haul more.
In the east, Asian elephants have been used to transport people and goods for thousands of years. Historically they have been a major feature of the logging industry, hauling heavy hardwoods through the difficult jungle terrain. According to the Food and Agricultural Organization of the UN, it is common for an elephant working in Sri Lanka's logging operations to haul 3 or 4 tonnes a day.
John Hutchinson of the Royal Veterinary College in London, UK has studied the locomotion of Asian elephants. He attributes their strength to several specialisations.
In terms of sheer tonnage, elephants may well be the strongest animals alive
While many mammals' skeletons account for around 10% of their body weight, the figure is closer to 20% for elephants, meaning they have a more robust frame. Hutchinson also says that their straighter limbs enable them to resist the downward force of gravity better, and to hold their own bulk plus any load.
Then there is the remarkable trunk. It contains no bones or cartilage, instead comprising up to 150,000 bundles of muscle fibres. The multi-use appendage allows elephants to communicate over vast distances, grasp individual twigs, reaffirm social bonds – and lift significant weights.
As with our own strength records, the maximum weight lifted by an elephant is a bit of a grey area. Still, a large bull is thought to be able to lift a log weighing up to 300kg with just its trunk. African elephants can weigh a tonne more than their Asian counterparts, so they may well be even stronger.
In terms of sheer tonnage, elephants may well be the strongest animals alive. But of course, they are pretty big themselves. Arguably the strongest animals are actually the smallest.
Ants are famously among the best super-atom-weight powerlifters in the world. Their prowess differs between species, but some can lift 10 to 50 times their bodyweight.
It is common for an elephant working in Sri Lanka's logging operations to haul 3 or 4 tonnes a day
In 2010, an Asian weaver ant (Oecophylla smaragdina) was photographed lifting 100 times its mass by researchers at the University of Cambridge.
While humans rely on hefty back muscles and elephants use their trunks, ants depend on their powerful mandibles for the real heavy lifting. Trap-jaw ants (Ondontomachus) have such powerful muscles in their mandibles, if they hold the mandibles against the ground and snap them shut they can launch themselves into the air.
There is another group of insects with a talent for weightlifting: beetles.
Any insect named for the ancient demi-God Hercules can be expected to have a reputation for super-strength. But the oft-repeated tale that the Hercules beetle (Dynastes hercules) can lift 850 times its body weight is as unsubstantiated as Paul Anderson's record-breaking back lift.
The Hercules beetle belongs to a group known as the rhinoceros beetles. Determined to find out the truth, locomotion expert Rodger Kram, now at the University of Colorado Boulder, put another kind of rhinoceros beetle to the test. He found they could only carry up to 100 times their bodyweight.
The mite can hold 1,180 times its own weight
In 2010, a new world's strongest beetle was crowned. Just like all the stories of human champions from humble backgrounds, it has an unglamorous existence surrounded by manure. The horned dung beetle (Onthophagus taurus) can pull up to 1,141 times its own weight.
Rob Knell of Queen Mary, University of London in the UK discovered the dung beetles' prowess while researching their mating tactics. The males use their horns to beat rivals, driving them out of tunnels and away from females.
The horned dung beetle's proportional strength is rivalled only by the oribatid mite (Archegozetes longisetosus). It is microscopic, weighing just 100 micrograms, and lives in the soil of forest floors. In 2007 researchers found it can hold 1,180 times its own weight and pull 540 times its own mass with its claws.
The extraordinary might of these tiny creatures is down to a quirk of physics.
The pioneering scientist Galileo Galilei had it right in his 1638 book Two New Sciences, in which he wrote that smaller animals are proportionately stronger and more robust than larger ones. It all comes down to strength-to-weight ratios.
Scaled up to human size, an ant would be incredibly weak
A bigger beast may have bigger muscles, but a lot of their strength goes to supporting the animal's own weight, so there is not much left over to lift additional weight. In contrast, tiny creatures have less mass to carry around, so they can dedicate more of their muscle power to weightlifting.
There are some additional biological factors that favour small animals. For example, the larger the animal, the more energy it needs to sustain essential functions like respiration and blood circulation. With simpler and more compact internal systems, smaller animals like beetles can invest more of the energy they gain from food into building strong exoskeletons, which bear weight better than soft tissue.
This means that, while insects can display amazing proportional strength, you cannot scale up an ant to human size and expect it to retain its power.
As the ant swelled, its mass would increase in line with its volume, so the dimensions would be cubed. But its strength comes from the surface area of the muscles, which would only be squared.
The King Kong idea doesn't work, and neither do giant killer ants
"Scaled up to human size, an ant would be incredibly weak, because the cross-sectional area of its legs would have increased much less than the volume of its body," says biologist and BBC Earth contributor Claire Asher. "It wouldn't even be able to stand. And, much worse, it wouldn't be able to breath either. Ants use tiny holes called spiracles to circulate oxygen into their bodies, but scaled-up to human size these tubes would be too small to provide oxygen to the entire body."
These principles apply to all animals, and mean that each body type can only work within a limited range of sizes. "The King Kong idea doesn't work, and neither do giant killer ants," says Asher.
This implies that today's strongest animals might be pretty representative of the strongest animals that have ever lived. Earth has been home to much bigger creatures than elephants – the largest dinosaurs dwarfed the elephants – but these huge beasts may not have been able to haul much more than the elephants do. Strength, it seems, has its limits.
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