And some of the newest participants are a little older than what might be expected for the extreme sport.
KOLR caught up with a woman in her mid-30s, who decided she wanted to do a triathlon.
Over the last year and a half, Lynn Johnson has run five sprint-length multi-sport races.
She says it's a sport that caters to people that aren't excessively athletic.
The U.S. Triathlon Association agrees. They say the fastest growing group of first time competitors are between 35 and 45 years old.