Swimming, like many sports, favors competitors who are lean and thin. Watch the Summer Olympic Games and check out the physical build of the swimmers competing there. They are tall with broad shoulders, but very small waists and flat stomachs. The women showcase similar builds. 

Swimmers have to carry around the body mass during the race. A lighter swimmer does not work as hard as a larger swimmer because they have less to carry around. This also applies to running and bicycling (see a pattern here...). The top runners and cyclists are not big burly athletes, but more like svelte and lean individuals, usually average height.

Recognizing this fact, and with the increasing popularity of triathlons here in the USA, the governing body here in the U.S., USA Triathlon, created a separate of competition for people who were larger than most of the field. They call the men "clydesdales" and women "athenas".

The Clydesdale and Athena competitive divisions are based on weight minimums outlined in the USA Triathlon Competitive Rules. Athletes competing in the Clydesdale division must be a minimum of 220 pounds and athletes in the Athena division must be a minimum of 165 pounds. -- USA Triathlon

So a man larger than 220 pounds is considered to be a Clydesdale. I definitely qualify for that status! As I was reading on the board Clydesdales/Athenas (200+ lb / 91+ kg), I read a thread where the poster referred to clydesdales that are even larger, say over 300 pounds, he called "uber clydesdales".

It was that moment that I adopted the term "uberclydesdale". Like the members at that site, I don't let nay-sayers keep me from working out and in my case, competing. I may not look like Ryan Lochte, but I'm out there doing it and loving every moment!