Michael Phelps’ much-anticipated race against a great white shark served up a double dose of disappoinment for viewers on Sunday night. Not only did Phelps swim against a fake hologram shark — but he lost to his opponent by two seconds.
To be fair, the odds were already stacked against Phelps: Great white sharks can reach top speeds of 25 to 35 miles per hour, while Phelps reached top speeds of only 5 to 6 miles per hour, even while wearing a monofin. Still, despite his loss — and the outpouring of ire on the internet — Phelps joked on Twitter that he’s down for a rematch, as long as it happens in a slightly toastier environment.
By racing in the waters off the coast of South Africa, the 23-time Olympic gold medalist experienced a significant drop in temperature compared to the balmy norm of Olympic standard swimming pools. While the waters surrounding the continent are generally warm, the southern tip of South Africa can be significantly colder. The average sea temperature around Cape Town is around 59 degrees Fahrenheit, which is 20 degrees colder than the mandated water temperature for Olympic swimming pools. The temperature during the race on Sunday was estimated to be a chilly 56 degrees.
The ideal water temperature for Phelps to race against a shark (simulated or otherwise) would be close to the Olympic standard of 77 to 82 degrees Fahrenheit. This temperature addresses most of the factors that can affect a swimmer’s performance. Water that’s too cold can cause muscles to cramp up and waste energy by creating heat, while water that’s too hot prevents a swimmer from getting rid of excess heat through sweat and can cause muscles to overheat.
Swimming in colder water increases a swimmer’s risk of getting hypothermia, which can obviously slow a swimmer down. In a review published in the journal Biology of Exercise in 2014, researchers explained that, because “water is a much better heat conductor than air,” humans easily lose body heat to cold water. In the cold, a person’s metabolic rate tends to increase in order to stay warm, and doing so takes up a lot of energy. In an interview with CNN in 2013, Professor Mike Tipton of the Human and Applied Physiology Department at the University of Portsmouth explained that, while cold water may give a swimmer an immediate, energizing jolt — that’s what makes polar bear dips so appealing — that feeling is actually a state of shock, and prolonging the experience may cause irregular heart rhythms.
Temperature also has an effect on the density of the water, which in turn can slow down any objects moving through it. Colder water is more dense than warm water (which is why open water gets colder with increased depth). But usually the effects of temperature on water density are negligible at the temperature ranges and depths that athletes usually encounter.
Of course, Phelps shouldn’t request a rematch in waters that are too warm, either, as they can lead to dehydration and even death for competitive swimmers. In a tragic accident in 2010, U.S. National Team swimmer Fran Crippen died after racing in a pool that was officially 84 degrees. Other competitors that swam in the pool reported that it felt even hotter, and many experienced swollen limbs and disorientation as a result. In a study published in the journal Science and Sports in 2011, researchers showed that swimmers lost more water weight through sweating when immersed in a pool that was 90 degrees than they did at 73 or 80 degrees Fahrenheit.
For Phelps, the key is to find a sea where the temperature is just right.
A good option for the 2018 sequel to Phelps versus Shark could be Honolulu, Hawaii — and not just because the average sea temperature off the coast of Honolulu hovers around a balmy, Olympic-ready 80 degrees. The waters there are home to various species of actual, not holographic, sharks, leaving Phelps and the Discovery channel team no excuse to broadcast another disappointing virtual race.