In 1920, the fastest sprinting record in 100 meters was 10.6 seconds. Many people thought it is the limit, and this record will never be broken, and it is beyond human capabilities. Slowly but surely, it kept breaking, and in 1968, multiple sprinters broke ten-second barriers, sprinting 100 meters in 9.9 seconds. Then again, people thought that is it; it is the limit. However, now in 2020, we have Usain Bolt, who currently holds 9.58 seconds record and is known as the fastest man on the planet. Even now, we can find some people saying that no one can break the current record. Is this true? What is the whole engineering behind running?
Why can’t humans run faster: Reasons
Humans are not the fastest animals, and this is obvious from our anatomy. For example, we have bulky, cold muscles that weigh down our legs. The calves must swing back and forth at every leg stroke and require much force to increase the steps’ frequency. Considering that our muscles have few fast trigger fibers, a frequency of about five steps per second, 300 steps per minute, will be the upper limit for our leg muscles’ capacity to contract and extend.
Cheetahs, ostriches, horses, dogs, and cats have all the leg muscles bundled way up their legs and connected to the lower point of action by long tendons. Therefore lower part of the rear legs is very light. They can swing at a much higher frequency. Their short muscles are closer to the hip rotation and do not have to move so much as a long leg muscle. The force needed to swing a large, muscle free and light leg is a lot less than the force needed to swing the massive muscular human leg. So this is the first reason why most mammals are faster than us.
We also have a relatively short foot. The foot is extra leverage that allows us to use the power of the calf muscles. When we walk, as opposed to running, the calf muscles are used very little. The foot acts as gear; the shorter and lighter the gear, the higher the force, but lower the speed. The human foot allows the calf muscle to exert much force on the toes but not much speed. A longer foot will provide less power but more speed, like a taller gear.
If we look at the runner animals like cheetah, horses, or even domestic dogs and cats, they all walk on their toes, and their feet are very long. Sometimes, as long as the other leg bones. Humans are like a motor vehicle with a gearbox stuck in the second gear. At the same time, runner animals benefit from a tall gear for fast running. So if we can swing our legs at a frequency of about five steps per second, each step can be 2.5 meters long. Then the top speed of a human cannot exceed 12.5 meters per second, equal to 45 km/h, no matter how strong our legs are. These numbers may apply to Usain Bolt.
How fast humans can theoretically run
For an average human, the maximum speed will be more like 30 km/h. However, the new research shows that if we manage time that applies force to the ground while sprinting, our limbs and muscles can go faster. Theoretically, we can run 64 km/h at the max. 64 Km/h is fast but not as much as fast running animals. A fit human cannot outrun a bear, let alone a horse or a large dog, but we theoretically can outrun all of them on the long distance.
Humans are often called weak and fragile animals that manage to get through the struggle for survival by their large brains, but it is not the whole story. It is not much appreciated that humans, given certain conditions, can outrun any land mammal on the long distance. We might not be the fastest, but we are the best marathon runners on the planet. How is that possible? It is because of the three extraordinary evolutionary traits of humans.
- We have the most efficient water cooling system in the animal world.
- We are the only animal with a two gear shifter.
- We are among the very few land animals to have hind legs.
Water cooling system of human muscles
Muscles, like all engines, produce heat. The chemical energy they receive from the blood cannot be entirely converted into mechanical energy, and the rest becomes heat. Heat is good for us as we are a homeothermic, hot-blooded species. Our body temperature must be comprised within a very narrow range to allow us to live and thrive. If not sufficiently dissipated, too much heat will raise the body temperature and put our survival at risk.
The muscles of a mammal have an efficiency of about 18 to 26 percent. In simple words, 18 to 26 percent of the energy that comes from the blood is converted into mechanical energy. The remaining 74 to 82 percent is either not drawn from the blood or is converted into heat. It is a complicated task to dissipate heat adequately. Mainly heat is dissipated through the skin, and the surface of the skin is just too much.
As our body grows, its volume increases with its linear dimensions’ cubic power. Its outer surface increases only with the square power. If we double the length of an animal, all the rest remaining equal, its body volume will increase eight times and skin surface four times. A big animal will soon meet a body surface deficit to dissipate the heat produced by its muscles.
The evolutionary solutions to these problems are multiple. For example, elephants have developed large ears with a dense network of blood vessels that act as radiators to dissipate heat. Other animals limit the amount of heat they produce by reducing muscle metabolism. When they need to produce long-duration efforts, they start sweating.
How sweating help dissipate heat
Water requires much heat to evaporate. Almost 2300 joules or 450 calories per each gram of liquid water becomes vapor. Water does not have to be taken to its boiling point to evaporate. In essence, it can evaporate at any temperature if energy is given to it in different ways, for example, by a current of air that flows by its surface. Imagine having our skin always wet, and the current of air generated by running makes this layer of water evaporate. Continued sweating replaces the water that evaporates.
Every gram of water that evaporates will remove 2300 joules of heat from our skin, and our skin blood vessels will transfer heat from the blood to the skin and from there to the water. An athlete can produce as many as three liters of sweat per hour. This sweat corresponds to 3,000 grams, and if they all evaporate, they will require nearly 7 million joules of energy. If this is done in one hour, it is equal to almost two kilowatts of cooling power.
So we humans have a cooling system that can reach nearly 2 kilowatts of thermal power. It removes much of the heat produced by our muscles. It allows us to keep a body temperature stable, even under a continuous and intense muscular effort. Assuming a cooling efficiency of 100%, which is never achieved, we could ideally generate a continuous muscular power of 0.6 To 0.9 horsepower, so this is why we have no fur. Fur would insulate the sweat layer that lies on the skin, preventing the air current from making it evaporate.
Horses also sweat, but their fur, however short, is tough to evaporate water than on the bare skin of a human. Heat transmission is far worse across a thick layer of liquid water trapped in the fur, as anyone who has been sweating through a flannel shirt has experienced. Humans have the most efficient water cooling system in the animal world.
Humans’ two gear shifting
Humans can switch from plantigrade deambulation to digitigrade deambulation at will. When we walk, we place the entire foot on the ground, and we exploit the leverage offered by the length of the foot only to lift the weight of the leg a short distance. We almost do not use our calf muscles to walk. Because less muscle mass is used, less energy will be consumed, and less heat is produced. Walking is a slow but incredibly energy-efficient way to move.
Cats, dogs, horses, and all other running animals always move on their toe tips, no matter how slow they want to go. They cannot put their calf muscles at rest, and their slow walking pace is not that efficient. When humans run, we shift to a higher gear. We do not put the whole sole of our feet on the ground anymore, and we run on our toes. We mostly use the toes as balancers.
This way, the calf muscles can generate a strong force acting on the leverage provided by the foot’s length to lift the body’s entire weight. We can sufficiently use many more muscles when running than when walking. So we have two gears, a light one for energy-efficient slow walking and a strong one for fast and robust running or climbing. Although all species adapted to running never became fast runners, a long foot is necessary for fast running, rather than awkward and useless when walking in the first gear.
The secret ingredient: Hind legs
Last but not least, the third reason is unique among mammals. We walk solely on our hind legs. We share this ability, only with running Birds. Most two-legged animals use all four legs and occasionally walk on their hind legs, for example, bears, apes, monkeys, and lemurs.
Australians might dispute that kangaroos and wallabies are also bipedal, but the fact is, they do not walk at all. Instead, their evolution led to an even more radical transformation. They became a two-legged pogo stick where the two legs can only move simultaneously as they were one. By all means, kangaroos and wallabies are one-legged deambulators, at least from a functional perspective.
The ultramarathon runners of the planet
Humans became the ultramarathon runners of the animal kingdom by evolution. No other animal can run for eight hours at an average speed of 16 km/h in a hot climate. A horse can run much faster than a man, but after one hour, they have to stop and cool off in a warm climate or die from a heart stroke. In a cold environment, the problem of body heating is not relevant. Sled dogs can run for 200 kilometers at sub-zero temperatures, and also horses travel longer and faster in the cold. However, humans are unbeatable for their endurance in a hot climate.
Arabic camels are often stated as one of the best endurance runners of the animal kingdom. They have a different strategy from men to endure efforts like horses. They cannot sustain strong efforts for long. Camels are designed to spear water because of the environments they wander. They cannot afford to sweat as we do. If they do, their body temperature will rapidly increase and overclock.
A camel can travel for eight to ten hours, but at the speed of a fast walking human, a human can also do that. Most people in a caravan of camels crossing a desert walk alongside the camels, but humans can also do better. They can run the same distance in less time than a camel.
During the Great Australian camel race held in 1988, the winner walked and ran alongside his camel for 3,200 kilometers from Arras rock to Gold Coast. Humans and camels had the same long-distance performance, all thanks to sweating, legs allowed to post efficient, walking and running, and bipedal deambulation.
Pronghorn antelopes are the only animal that can compete against humans in the long run. Pronghorns can run at 50 kilometers per hour for three to four hours at a stretch. If the need arises, it can cruise at 70 kilometers per hour. The windpipe of a Pronghorn is twice as wide as ours. Compared to a goat of a similar size, its lungs are three times larger. All that oxygen is absorbed by a larger blood volume and pumped by an enormous heart. As a result, a Pronghorn can process five times more oxygen than a typical mammal and three times more than a human runner.
Additionally, an enormous heart and lungs mean the stomach is smaller. If the stomach is full or half food inside, running a marathon is extremely hard. Pronghorns in Wyoming perform a 250 to 500 kilometers yearly migration that takes them about three to four days, for the whole pack, young and old.
Nevertheless, the evidence for the argument that humans are the best at endurance running is that in 2005, Dean Karnazes had run 563 kilometers without ever stopping. He ran for 80 hours, 44 minutes without a break. It was utterly insane, and also, no other mammal can do that. Many ultramarathon runners run for hundreds of miles in a short period, which solidifies the argument that humans are the best endurance runners on the planet.
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