I did triathlons for awhile. Aspired to Hawaii Ironman, but never got there. Got to training regularly at 1/2 Ironman distance, which is run 13.1 miles, bike 56 miles, swim 1.2 miles.
Two events training per day, 6 days a week, 3 on the 7th day. I ran my fastest marathon, while doing triathlon training. Down the road in San Diego County is one of the international meccas of triathlon training.