25K Swim vs. 100K Run - Which Is Harder?

After observing some of the world's best swimmers perform at the World Open Water Swimming Championships, we wondered what is the equivalent of a 25K (15.5-mile) marathon swim on land?

While it is never a perfect comparison and it depends on each individual, the general consensus is that a mile of swimming is equal to 4-5 miles of running.

So if that is the case, then a 25K swim would be equal to a 100K run. If we throw in water and air temperature into the mix, then these distances may change. For example, if the water temperature went from 20°C (68°F) to 10°C (50°F), then swim would become much more difficult or if the air temperature went from 20°C (68°F) to 30°C (86°F), the run would become more difficult.

But if we held water conditions (e.g., rough) and humidity on land (e.g., high) constant, then is a 25K marathon swim equal to a 100K marathon run?

Are perspective tells us that this answer is off.

How do you measure difficulty? What is difficult to one person is not as difficult to another. Can we measure difficulty over the spectrum of humanity?

That is, how many people in the entire world can swim 25K - at whatever pace - and how many people can run - at whatever pace - 100K?

If we consider that slightly over 1,500 people have swum the English Channel since 1875, slightly over 175 people have swum the Catalina Channel since 1927 and an estimated 1,100 people have swum the Strait of Gibraltar, Tsugaru Channel, Cook Strait, Rottnest Channel and various well-known courses in lakes around the world (e.g., Zurich, lac St-Jean, lac Mempremagog) since 1928, the number of living people who can swum 25K is a relatively small number.

Add another 2,500 masters swimmers, lifeguards, fit endurance swimmers and others to the mix, and total number of people capable of swimming 25K is tiny - infinitesimal - relative to the number of people capable of running 100K.

So what is the comparable land distance of 25K?

We think it has to be a lot longer than 100K.

Photo of the 2010 World 25K Open Water Swimming Championships by Dr. Jim Miller.

Copyright © 2010 by Open Water Source