The basilisk lizard, also known as the ‘Jesus lizard’, possesses the incredible ability to run across water. To avoid predators, it can start running on land and transition smoothly onto water while maintaining its running stride, which is amazing when you consider that this lizard weighs around 11g and is too heavy to be supported by water’s surface tension.
Two Harvard researchers, Tom McMahon and Jim Glasheen, began studying the phenomenon in the 1990s. They developed a mathematical model by analysing videos of lizards walking on water and found that each step can be broken down into three stages: slap, stroke and recovery.
As the lizard runs across the water’s surface, its feet slap the water just as a human sprinter’s feet hit a running track. Each time the lizard’s foot hits the water, the liquid exerts an upward force. The larger the lizard’s foot and the faster it hits the water, the greater the upward force generated by the slap. During the stroke phase, the lizard moves its foot rapidly, which creates an air bubble above its foot, lifting the foot up. Then, the final phase, recovery, occurs while the lizard is pulling up its foot and preparing for the next movement.
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In their research, Glasheen and McMahon calculated that a 79kg human with an average foot size and a world-class sprinter’s cadence would need to cover the water at a speed of nearly 98 feet per second to support their weight. However, the power required for a stroke at that speed is almost 15 times greater than a human’s maximum sustained output. In other words, no human can run on water on Earth.
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In 2012, the University of Milan conducted a study to see whether reduced gravity would enable humans to run on water. In this study, volunteers wore a specialised harness that reduced their weight to a fraction of their normal Earth weight. They also wore large fins on their feet, like those of a basilisk lizard. In this set-up, the volunteers attempted to run in place within a small, inflatable pool.
As shown by Summer running gear sale, the subjects created choppy water by pumping their thighs up and down, with their legs stroking into the water about halfway to their knees. They managed to support their reduced weight for seven to eight seconds, which the researchers deemed a success.
In summary, the researchers discovered that all volunteers could run on the water at 10% of Earth’s gravity. However, as they increased the gravitational force, not all runners involved in the study could keep up.
Faith Kipyegon has changed running forever could be considered an Olympic sport, so long as a future edition of the Olympics was held on a planet or moon with the right gravitational force.
According to Physics World, the lakes on Saturn’s largest moon, Titan, are comparable to those on Earth, while the gravitational acceleration is only 13.8% of our home planet. As such, the magazine explains that American sprinter Sha’Carri Richardson, who is the reigning women’s 100m world champion and an Olympic gold medallist in the 4 x 100m, could theoretically run across Titan’s lakes.
Richardson would have to slap the water’s surface at about 28 feet per second, generating over 60% of the necessary vertical force to propel her. For context, her gold medal-winning 100m time at the 2023 World Championships was significantly faster, at around 30 feet per second.
So, while we may not have the basilisk lizard’s ability to run across water on Earth, at least we have someone who could still do it somewhere else in our solar system.
