The Ironman triathlon coming to Chattanooga, Tenn., in September sold out 2,500 slots in under a minute.

The Hits triathlons feature races exactly as demanding: a 2.4-mile swim, 112-mile bike and 26.2-mile run. The events have averaged just 30 registrants this year.

It's hard to see much difference between the two beyond the logo.

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